fixes handling of fancy nested classes in runtime reflection

Replaces the `jclazz.isMemberClass` check for whether we have an
inner/nested class with `jclazz.getEnclosingClass != null`, because there
exist classes produced by javac (see the attached jar file and the test log)
which have the following properties:
  * They are nested within a parent class
  * getEnclosingClass returns a non-null value
  * isMemberClass returns false

Previously such classes were incorrectly treated as non-nested, were
incorrectly put into an enclosing package rather than an enclosing class,
and had their names trimmed in the process, leading to situations when
a package has multiple declarations with the same name. This is now fixed.

When changing the check, we need to be careful with interpretation of
what Class.getEnclosingXXX methods return. If getEnclosingClass produces
a non-null result, this doesn't mean that the class is inner or nested,
because getEnclosingClass is also not null for local classes (the ones
with getEnclosingMethod != null || getEnclosingConstructor != null).
This is expressed in the order of pattern match clauses in `sOwner`.

Now when the bug is fixed, I also revert b18a2f8798b2, restoring a very
important integrity check in runtime reflection, which I had to disable
a couple hours ago to fix a master breakage. More details at scala-internals:
https://groups.google.com/forum/#!topic/scala-internals/hcnUFk75MgQ
SI-6840 fixes weird typing of quasiquote arguments

Previously quasiquote arguments were type checked against Any
which caused weird inference that made splicing of complex expressions
unusable:

   val l1 = List(q"foo")
   val l2 = List(q"bar")
   q"f(..${l1 ++ l2})" // argument type checked as Any instead of List[Tree]

This is fixed by forcing compiler to type check against type
variable which itself isn't used in any other way.
SI-7519: Additional test case covering sbt/sbt#914
SI-7020 Deterministic warnings for pattern matcher, take 2

The previous swing at determinism, ebb01e05cbe4, made decent
contact but apparently didn't hit it out of the park. The test
wavered every hundred or so runs, as witnessed occasionally in
nightly builds or pull request validation.

I setup a test to run neg/7020.scala a few hundred times, and
could trigger the failure reliably.

I then swept through the pattern matcher in search of HashMap and
HashSet creation, and changed them all to the Linked variety.
The results of that are published in retronym#ticket/7020-3 [1].

This commit represents the careful whittling down of that patch
to the minimal change required to exhibit determinism.

[1] https://github.com/retronym/scala/compare/ticket/7020-3
better macro impl shape errors

With the advent of quasiquotes, we allowed both arguments and return types
of macro impls to be c.Tree's (as opposed to traditional c.Expr[T]'s).

This warrants an update of macro def <-> macro impl signature mismatch
errors that include a printout of suggested macro impl signatures. Now
along with a signature that contains exprs, we suggest another signature
that has all exprs replaced by trees
Merge pull request #3057 from xeno-by/topic/fancy-java-classes

fixes handling of fancy nested classes in runtime reflection
Merge pull request #3060 from harrah/t7519-b

SI-7519: Additional test case covering sbt/sbt#914
Merge pull request #3068 from retronym/ticket/7020-3-1

 Deterministic warnings for pattern matcher, take 2
Merge pull request #3070 from xeno-by/topic/macro-impl-wrong-shape

better macro impl shape errors
Merge pull request #3059 from densh/pull/si-6840

SI-6840 fixes weird typing of quasiquote arguments