TailRec phase and tests for it.

Ported tailcall phase from scalac with such changes:
  - all transformation is done in the phase itself
     (previously half of the work was done in backend)
  - it is now able to run before uncurry
  - it is now a treeTransform
  - renamed to tailrec to make it more obvious that
     this phase transforms only recursive calls.

For now this is a single phase which speculatively
transforms DefDefs.
Speculation can be potentially removed by
splitting into 2 phases:
  one detecting which methods should be transformed
  second performing transformation.

But, as transformation requires as same amount of work
as detection, I believe it will be simpler to maintain
it as a single phase.

Conflicts:
	tests/pos/typers.scala

1 files changed, 0 insertions, 6 deletions

diff --git a/tests/untried/pos/t4649.scala b/tests/untried/pos/t4649.scala
deleted file mode 100644
index 0d6caa8d7..000000000
--- a/tests/untried/pos/t4649.scala
+++ /dev/null
@@ -1,6 +0,0 @@
-object Test {
-  // @annotation.tailrec
-  def lazyFilter[E](s: Stream[E], p: E => Boolean): Stream[E] = s match {
-    case h #:: t => if (p(h)) h #:: lazyFilter(t, p) else lazyFilter(t, p)
-  }
-}