Fix minor issue with CompilerPass.java

* This doesn't affect correctness, but use the right signature.
Change signature of CompilerPass.invalidate

* Return true/false depending on whether invalidation is possible
  or not.
Fixes to resetState in IRScope + invalidation in compiler passes.

* Use the new shiny invalidation method to reset state properly.
Merge branch 'master' into non-indy-jit
Minor tweak.

* That last computeScopeFlags in prepareForCompilation should not
  be necessary.