Avoid a compiler abort when people put a period in the middle of a clause.

The abort was caused by the fact that when the parser found an item that
looks like a fact for an undeclared predicate, such as the predicate ','/,
it created a hlds_pred filled with a clause_info in which terms that the
user intended to be goals are instead taken to be terms. Any reference
to predicates in those terms are taken by purity-checking to be higher order
references, which need a mode declaration. If the reference is to a predicate
(such as ,/2) whose declaration is implicit, that mode declaration will be
missing.

The fix has two parts. First, do not generate an abort in purity checking
when finding the mode declaration of a predicate or function in (what seems to
be) a higher order term is missing. Second, do not generate implicit
declarations for ,/2, since this is NEVER what the user wants.

A third part of this diff is an improvement in the contexts we record
for terms, for better error messages. I noticed the need for this when
looking at the compiler's output for the new cases.

compiler/post_typecheck.m:
   When finding an apparent reference to a predicate or function with
   no mode declarations, do not abort; instead, report an error.

compiler/purity.m:
   Record the error reported by post_typecheck.m.

compiler/add_clause.m:
   If we see a clause for `,'/2, do NOT treat it as implicitly defining
   a ,/2 predicate. Instead, generate a situation-specific error message that
   mentions the usual cause of the error.

compiler/add_pred.m:
   Clean up the predicates that add the implicit predicate declarations
   by making them both update module_infos, and by putting their arguments
   into a consistent order.

compiler/make_hlds_passes.m:
   Do likewise for a couple of predicates here.

compiler/add_pragma.m:
   Conform to the change to add_pred.m.

compiler/superhomogeneous.m:
   When expanding a term such as

      line 1: p(a,
      line 2: p(b,
      line 3: c))

   associate line 2 with the unification of a fresh variable with b,
   and line 3 with the unification of a fresh variable with c. We used
   to use the context of the top level term, which in this case is line 1,
   instead.

   This makes the compiler generate better (less misleading) output for the
   ref_to_implicit_pred.m test case below, as well as in many other cases.

compiler/state_var.m:
   When replacing !.X or !:X with a fresh variable term, copy the context
   of the original functor term to the new variable term. Before the change
   to superhomogeneous.m, this wasn't needed since the context of that term
   was ignored, but now we use it.

tests/invalid/ref_to_implicit_pred.{m,err_exp}:
   New test case to test the first part of the fix.

tests/invalid/ref_to_implicit_comma.{m,err_exp}:
   New test case to test the second part of the fix.

tests/invalid/Mmakefile:
   Enable both new test cases.

tests/hard_coded/impl_def_literal.{m,exp}:
   Update this expected output for the more accurate contexts we now
   generate, and update the comment in the source code accordingly.

tests/invalid/ambiguous_overloading_error.exp:
tests/invalid/max_error_line_width.err_exp:
tests/invalid/transitive_import_class.err_exp:
tests/warnings/ambiguous_overloading.exp:
   Update these expected outputs for the more accurate contexts we now
   generate.
Fix Mantis bug 314 for temp frames created by nondet procedures.
Also fix some bugs in related code, and improve the related debugging
infrastructure.

-------------------

runtime/mercury_stacks.[ch]:
   Fix bug 314 for temp frames created by nondet procedures. The fix will
   probably also work for *det* procedures that create temp frames on the
   nondet stack, but I can't think of a way to test that, because det
   procedures create such frames only in very specific circumstances,
   and I cannot think of a way to nest a recursive call inside those
   circumstances.

   The problem was that when we were creating new temp frames on
   the nondet stack, we did not check whether the current nondet stack segment
   had room for them. We now do.

   The stack trace tracing code needs to know the size of each nondet stack
   frame, since it uses the size to classify frames as temp or ordinary.
   The size is given by the difference in address between the address of the
   frame and the address of the previous frame. This difference would yield
   an incorrect size and hence an incorrect frame classification if a temp
   frame were allowed to have a frame on a different segment as its
   immediate predecessor.

   We prevent this by putting an ordinary (i.e. non-temp) frame at the bottom
   of every new nondet stack segment as a sentinel. We hand-build this frame,
   since it is not an "ordinary" ordinary frame. It is not created by a call,
   so it has no meaningful success continuation, and since it does not make
   any calls, no other frame's success continuation can point to it either.

   If backtracking reaches this sentinel frame, we use this fact to free
   all the segments beyond the one the sentinel frame is in, but keep the
   frame the sentinel frame is in, since we are likely to need it again.

   Document the reason why MR_incr_sp_leaf() does not have to check
   whether a new stack segment is needed. (See the fix to llds_out_instr.m
   below.)

runtime/mercury_stack_trace.[ch]:
   When traversing the nondet stack, treat the sentinel frame specially.
   We have to, since it is an ordinary frame (i.e. it is not a temp frame),
   but it is not an "ordinary" ordinary frame: it does not make calls,
   and hence calls cannot return to it, and it does not return to any
   other frame either. It therefore does not have the layout structures
   (label and proc) that the nondet stack traversal expects to find.

   Fix an old bug: the nondet stack traversal used a simple directional
   pointer comparison to check whether it has reached the bottom of the nondet
   stack. This is NOT guaranteed to work in the presence of stack segments:
   depending on exactly what addresses new stack segments get, a stack frame
   can have an address BELOW the address of the initial stack frame
   even if it is logically ABOVE that stack frame.

   Another old bug was that a difference between two pointers, which could
   be 64 bit, was stored in an int, which could be 32 bit.

   The nondet stack traversal code used a similar directional comparison
   to implement optionally stopping at an arbitrary point on the nondet stack.
   Fixing this facility (the limit_addr parameter of MR_dump_nondet_stack)
   while preserving reasonable efficiency would not be trivial, but it would
   also be pointless, since the facility is not actually used. This diff
   deletes the parameter instead.

   Move some loop invariant code out of its loop.

trace/mercury_trace_cmd_developer.c:
trace/mercury_trace_external.c:
   Don't pass the now-deleted parameter to mercury_stack_trace.c.

runtime/mercury_wrapper.c:
   Record the zone of the initial nondet stack frame, since the fix
   of mercury_stack_trace.c needs that info, and it is much more efficient
   to set it up just once.

tests/hard_coded/bug314.{m,exp}:
   The regression test for this bug.

tests/hard_coded/Mercury.options:
   Compile the new test case with the options it needs.

tests/hard_coded/Mmakefile:
   Enable the new test case.

-------------------

runtime/mercury_wrapper.c:
   The compiler knows the number of words in a stack frame it is creating,
   not necessarily the number of bytes (though it could put bounds on that
   from the number of tag bits). Since this size must sync with the runtime,
   change the runtime's variable holding this size to also be in words.

   Note that similar changes would also be beneficial for other sizes.

compiler/llds_out_instr.m:
   Conform to the change in mercury_wrapper.c, fixing an old bug
   (mercury_wrapper.c reserved 128 BYTES for leaf procedures, but
   llds_out_instr.m was using that space for procedures whose frames
   were up to 128 WORDS in size.)

compiler/mercury_memory.c:
   Conform to the change in mercury_wrapper.c.

-------------------

runtime/mercury_memory_zones.h:
   Instead of starting to use EVERY zone at a different offset, do this
   only for the INITIAL zones in each memory area, since only on these
   is it useful. When the program first starts up, it WILL be using
   the initial parts of the det stack, nondet stack and heap, so it is
   useful to make sure that these do not collide in the cache. However,
   when we allocate e.g. the second zone in e.g. the nondet stack, we are
   no more likely to be beating on the initial part of any segment
   of the det stack than on any other part of such segments.

   If a new debug macro, MR_DEBUG_STACK_SEGMENTS_SET_SIZE is set (to an int),
   use only that many words in each segment. This allows the segment switchover
   code to be exercised and debugged with smaller test cases.

runtime/mercury_conf_param.h:
   Document the MR_DEBUG_STACK_SEGMENTS_SET_SIZE macro.

   Convert this file to four-space indentation with tabs expanded.

-------------------

runtime/mercury_overflow.h:
   Make abort messages from overflows and underflows more useful by including
   more information.

runtime/mercury_overflow.c:
   Add a new function to help with the better abort messages.
   Since this file did not exist before, create it.

runtime/Mmakefile:
   Add the new source file to the list of source files.

-------------------

runtime/mercury_debug.[ch]:
   Fix problems with the formatting of the debugging output from existing
   functions.

   Add new functions for dumping info about memory zones.

   Factor out some common code.

   Convert the header file to four-space indentation.

-------------------

runtime/mercury_grade.c:
   Generate an error if stack segments are specified together with stack
   extension

-------------------

trace/.gitignore:
util/.gitignore:
tests/debugger/.gitignore:
   List some more files.

-------------------

runtime/mercury_context.c:
runtime/mercury_engine.[ch]:
runtime/mercury_misc.h:
compiler/notes/failure.html:
   Fix white space.
Fix comment.
Fix breakage.

runtime/mercury_stacks.c:
   Fix typo.
Only define MR_nondetstack_inclusion_check in low-level C grades.

runtime/mercury_overflow.c:
	As above: compiling this function in high-level C grades
	will fail since it refers to fields of the MR_Context
	structure that do not exist in those grades.
Merge remote-tracking branch 'upstream/master' into feature-extras-lex-op