brings JavaMirrors up to speed with ClassfileParser

Apparently there are still discrepancies between how the vanilla compiler
turns class files into symbols and how the reflective compiler does it.

Working on bringing these guys in sync, one bug at a time.
Merge pull request #2761 from scalamacros/ticket/7510

Assorted toolbox fixes
SI-7694 @uncheckedBounds, an opt-out from type bounds checking

Synthetic defs introduced by transforms like named/default arguments,
ANF (in scala-async) often introduce a type tree (the tpt of the temporary)
that are based on the types of expressions. These types are scrutinized in
RefChecks to check that type parameter bounds are satisfied.

However, the type of the expression might be based on slack a LUB that
fails to capture constraints between type parameters.

This slackness is noted in `mergePrefixAndArgs`:

	// Martin: I removed this, because incomplete. Not sure there is a
	// good way to fix it. For the moment we just err on the conservative
	// side, i.e. with a bound that is too high.

The synthesizer can now opt out of bounds by annotating the type as follows:

   val temp: (<expr.tpe> @uncheckedBounds) = expr

This facility is now used in named/default arguments for the temporaries
used for the reciever and arguments.

The annotation is hidden under scala.reflect.internal, rather than in
the more prominent scala.annotation.unchecked, to reflect the intention
that it should only be used in tree transformers.