Eliminate JavaRepeatedParamClass

Having two repeated param classes (and two types) does not work,
because we need to maintain an overriding relationship between
Scala repeated param methods and Java repeated param methods (this
will be resolved later by bridges).
Adapt signature of <repeated>

so that sig(<repeated>[T]) = sig(Seq[T]).
Add varargs bridge methods

Distinguish translations between Java and Scala varargs methods
and add bridges where needed.
Fixed tpd.ref

Did not work for this prefixes and other singleon types before.
I.d. was generating a SelectFromType tree, which is wrong.
Fixed underlyingIfRepeated.

... and moved to TypeApplications.
Cleanup for varargs bridge.

Now inserts a bridge whenever a method overrides a Java varargs method.
This is conservative but safe. We might use a more aggressive scheme, as
the one in Scala 2, but it's not clear the win would warrant it.
Added test case for varargs bridges

Currently we cannot run this test automatically because the testing framework
does not know about .java files. It was run manually and verified that ElimRepeated
does was it is supposed to do (create a varargs bridge).
Merge pull request #141 from dotty-staging/transform/repeated

Transform/repeated