c.typeCheck(silent = true) now suppresses ambiguous errors

Otherwise use cases like the one shown in the attached test (trying to
typecheck something, which leads to an ambiguous overload error) will
mysteriously fail compilation.
Corralling Modes into a smaller pen.

Attempting to reduce the frequency of low-level operations
with modes. I mean stuff like this:

  if ((mode & (EXPRmode | LHSmode)) == EXPRmode)

THey don't make those ten line boolean guards any easier
to understand. Hopefully this will lead us toward eliminating
some of the modes entirely, or at least better isolating
their logic rather than having it interspersed at arbitrary
points throughout the typer.

Modes are in their entirety a leaked implementation detail.
Typing a tree requires a tree and optionally an expected type.
It shouldn't require a bucket of state bits. In subsequent
commits I will start eliminating them.

This commit also breaks adapt down into more digestible chunks.
Started eliminating modes.

Consolidating the scattered typer state in Context, where it's
relatively easy to keep an eye on, rather than threaded throughout
the typer in sneaky/sticky bitmasks. The general pattern will be
what was once an explicitly passed around bit in Mode becomes
an implicitly propagated-as-appropriate bit in Context.

In this commit:

          ALTmode becomes context mode "PatternAlternative"
         STARmode becomes context mode "StarPatterns"
  SUPERCONSTRmode becomes context mode "SuperInit"
Eliminated SNDTRYmode.

It becomes context mode "SecondTry".
Eliminated RETmode.

It becomes context mode "ReturnExpr".
Eliminated HKmode.

It becomes context mode "TypeConstructor".
Refactored stabilize.

Mode elimination ramps up in difficulty now, so I pursued
other forms of code hygiene.
Incorporated reviewer feedback.

Made things a little more consistent and self-apparent.
Merge branch 'master' into HEAD

* master:
  SI-7469 Remove @deprecated scala.util.logging
  SI-3943 Test case for already-fixed Java interop bug
  Fix formatting for couple of docs in the compiler
  SI-7476 Add documentation to GenericTraversableTemplate
  SI-7469 Remove @deprecated scala.util.parsing.ast
  SI-7469 Remove @deprecated MurmurHash elements
  SI-7469 Remove deprecated elements in s.u.parsing.combinator
  SI-7469 Make @deprecated elems in scala.concurrent private[scala]
  removes duplication in inferImplicitValue
  SI-7047 fixes silent for c.inferImplicitXXX
  SI-7167 implicit macros decide what is divergence
  macroExpandAll is now triggered in all invocations of typed
  SI-5923 instantiates targs in deferred macro applications
  SI-6406 Restore deprecated API
  SI-6039 Harden against irrelevant filesystem details
  Limit unnecessary calls to Type#toString.
  fix typo in comment
  SI-7432 add testcases
  SI-7432 Range.min should throw NoSuchElementException on empty range
  AbstractFile.getDirectory does not return null when outDir is "."

Conflicts:
	src/compiler/scala/tools/nsc/typechecker/Typers.scala
Incorporated reviewer feedback.

Made things a little more consistent and self-apparent.
SI-7494 Each plugin must only be instantiated once.

The old behavior was that Plugin.loadAllFrom took a distinct
list of plugin locations.

The broken behavior incorrectly punted to the pruning
algorithm in Plugins.loadPlugins$pick.

The new behavior is to distinctify the list of class names
to load.

This is more robust; under the old scheme, specifying the
continuations.jar under two file names would fail as
described in the ticket.

Pruning a plugin by disabling (-Xplugin-disable) or because
it steps on someone else's phase name suffers the same
defect. There is no way to tell the plugin it has been
benched. And you know that global I gave you?  Can I
have it back?
Merge commit 'd93826f278' into pr/enter-elimination-mode

* commit 'd93826f278':
  Incorporated reviewer feedback.
  Incorporated reviewer feedback.
  Refactored stabilize.
  Eliminated HKmode.
  Eliminated RETmode.
  Eliminated SNDTRYmode.
  Started eliminating modes.
  Corralling Modes into a smaller pen.

Conflicts:
	src/compiler/scala/tools/nsc/typechecker/Macros.scala
	src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
	src/compiler/scala/tools/nsc/typechecker/Typers.scala
Reimplementing much of the DefaultPromise methods
Optimizations:
1) Avoiding to call 'synchronized' in tryComplete and in tryAwait
2) Implementing blocking by using an optimized latch so no blocking ops for non-blockers
3) Reducing method size of isCompleted to be cheaper to inline
4) 'result' to use Try.get instead of patmat
SI-7427 stop crashing under -Ydebug.

Change "dumpClassesAndAbort" to "devWarning". You can witness
it happen like so.

  % scalac test/files/pos/t7427.scala -Ydebug -Xdev
  ...
  [running phase cleanup on t7427.scala]
  [running phase icode on t7427.scala]
  warning: !!! PJUMP(method matchEnd4)/scala.tools.nsc.backend.icode.GenICode$PJUMP is not a control flow instruction
  warning: !!! PJUMP(method case6)/scala.tools.nsc.backend.icode.GenICode$PJUMP is not a control flow instruction
  [running phase inliner on t7427.scala]
  [running phase inlinehandlers on t7427.scala]

Having now lived with this for months, I have no ambition to
unravel the actual problem, I just want it to stop crashing.
Merge pull request #2565 from paulp/issue/7427

SI-7427 stop crashing under -Ydebug.
An attempt to make tests deterministic.

The nondeterminism presently showing itself in
presentation/implicit-member is a consequence of the
presentation compiler tests relying on details of the
behavior of toString calls. We need to stomp this out,
but it will take a while. Based on the check file
changes enclosed with this commit, this will suffice
for the presentation compiler tests. A broader assault
will have to take place, but not yet.
Merge pull request #2566 from paulp/pr/nondeterminism

An attempt to make tests deterministic.
Merge remote-tracking branch 'origin/master' into pr/enter-elimination-mode

* origin/master:
  An attempt to make tests deterministic.
  SI-7427 stop crashing under -Ydebug.
SI-7494 Tests for status quo

Exploit SI-6446 fix to move old pending tests for plugins to the
active pool.

Also, nuance the partest runner to allow the compiler to crash
with a FatalError if a check file is present.

Some of the plugin tests make phase assembly throw.

One of the legacy tests was moved back to pending:

There seems to be a race for who shall be deemed truly dependent.

Back to pending for you!

apm@mara:~/projects/snytt/test$ ./partest files/neg/t7494-cyclic-dependency/
Selected 1 tests drawn from specified tests

> starting 1 test in neg
ok 1 - neg/t7494-cyclic-dependency

1/1 passed (elapsed time: 00:00:04)
Test Run PASSED
apm@mara:~/projects/snytt/test$ ./partest files/neg/t7494-cyclic-dependency/
Selected 1 tests drawn from specified tests

> starting 1 test in neg
!! 1 - neg/t7494-cyclic-dependency               [output differs]
> 0/1 passed, 1 failed in neg

>>>>> Transcripts from failed tests >>>>>

> partest files/neg/t7494-cyclic-dependency
% scalac t7494-cyclic-dependency/ThePlugin.scala
% scalac t7494-cyclic-dependency/sample_2.scala
error: Cycle in compiler phase dependencies detected, phase cyclicdependency1 reacted twice!

% diff files/neg/t7494-cyclic-dependency-neg.log files/neg/t7494-cyclic-dependency.check
@@ -1 +1 @@
-error: Cycle in compiler phase dependencies detected, phase cyclicdependency1 reacted twice!
+error: Cycle in compiler phase dependencies detected, phase cyclicdependency2 reacted twice!

0/1 passed, 1 failed (elapsed time: 00:00:04)
Test Run FAILED
Moves AbstractFileClassLoader to scala-reflect.jar

Its string name was used in ReflectionUtils and became broken after repl
got factored out. This hints that that classloader belongs to where it is
used, i.e. to scala-reflect.jar.

Moreover AbstractFile is defined in scala-reflect.jar, so it's only
logical to also define a derived classloader in scala-reflect.jar.