Upgrade to Scala 2.11.0-M7.

And all the changes needed to adapt to the new internal API
of the compiler, and other small things.
WIP. Seems to work but not really sure.
Add support for SAM treatment of js.FunctionN.
Optimize away scalaFun2js(jsFun2Scala(function() ...)).

The rewriting of Scala functions as JS anonymous functions
wraps them in AnonFunctionN. The implicit conversion from
Scala function to JS function now matches its argument
against the shape of tree produced by this rewriting, to
optimize it away instead of building the reverse wrapper
on top of it.
Add basic support for -Ydelambdafy:method.

This implementation does not take advantage of specialization.