parsers: rename YY_NULL as YY_NULLPTR to avoid conflicts with Flex

Flex also defines YY_NULL (to 0).  Avoid gratuitous conflicts.

* data/c.m4 (b4_null_define): Rename YY_NULL as YY_NULLPTR.

* data/glr.c, data/lalr1.cc, data/location.cc, data/variant.hh,
* data/yacc.c, src/parse-gram.c, tests/actions.at, tests/c++.at,
* tests/cxx-type.at, tests/glr-regression.at, tests/headers.at,
* tests/push.at, tests/regression.at:
Adjust.
aver: it is no longer "protected against NDEBUG"

Apply the same rules for aver as for assert: no side effects,
especially not important ones.

* src/AnnotationList.c, src/muscle-tab.c: Adjust aver uses to resist
to -DNDEBUG.
version 3.0.1

* NEWS: Record release date.
maint: post-release administrivia

* NEWS: Add header line for next release.
* .prev-version: Record previous version.
* cfg.mk (old_NEWS_hash): Auto-update.
skeletons: use better names when computing a "goto"

* data/glr.c (yyLRgotoState): Name the symbol argument yysym, instead
of yylhs.
* data/lalr1.cc (yy_lr_goto_state_): Likewise.
* data/lalr1.java (yy_lr_goto_state_): New, modeled after the previous
two routines.
Use it.
tests: simplify useless obfuscation

* tests/c++.at: $$ is not special for M4, there is no need to "escape"
it.
tests: check $$'s destruction with variant, YYERROR, and no error recovery

When variant are enabled, the yylhs variable (the left-hand side of
the rule being reduced, i.e. $$ and @$) is explicitly destroyed when
YYERROR is called.  This is because before running the user code, $$
is initialized, so that the user can properly use it.

However, when quitting yyparse, yylhs is also reclaimed by the C++
compiler: the variable goes out of scope.

This was not detected by the test suite because (i) the Object tracker
was too weak, and (ii) the problem does not show when there is error
recovery.

Reported by Paolo Simone Gasparello.
<http://lists.gnu.org/archive/html/bug-bison/2013-10/msg00003.html>

* tests/c++.at (Exception safety): Improve the objects logger to make
sure that we never destroy twice an object.
Also track copy-constructors.
Use a set instead of a list.
Display the logs before running the function body, this is more
useful in case of failure.
Generalize to track with and without error recovery.
lalr1.cc: fix the support of YYERROR with variants

When variant are enabled, the yylhs variable (the left-hand side of
the rule being reduced, i.e. $$ and @$) is explicitly destroyed when
YYERROR is called.  This is because before running the user code, $$
is initialized, so that the user can properly use it.

However, when quitting yyparse, yylhs is also reclaimed by the C++
compiler: the variable goes out of scope.

Instead of trying to be too smart, let the compiler do its job: reduce
the scope of yylhs to exactly the reduction.  This way, whatever the
type of scope exit (regular, exception, return, goto...) this variable
will be properly reclaimed.

Reported by Paolo Simone Gasparello.
<http://lists.gnu.org/archive/html/bug-bison/2013-10/msg00003.html>

* data/lalr1.cc (yyparse): Reduce the scope of yylhs.
* tests/c++.at: We now pass this test.
lalr1.cc: formatting changes

* data/lalr1.cc: Fix indentation.