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, 7 deletions

diff --git a/tests/untried/neg/t6574.check b/tests/untried/neg/t6574.check
deleted file mode 100644
index c67b4ed80..000000000
--- a/tests/untried/neg/t6574.check
+++ /dev/null
@@ -1,7 +0,0 @@
-t6574.scala:4: error: could not optimize @tailrec annotated method notTailPos$extension: it contains a recursive call not in tail position
-    println("tail")
-    ^
-t6574.scala:8: error: could not optimize @tailrec annotated method differentTypeArgs$extension: it is called recursively with different type arguments
-    {(); new Bad[String, Unit](0)}.differentTypeArgs
-                                   ^
-two errors found