Improve code comments for some ctx stuff

* in pp_return(), some comments were out of date about how
  leave_adjust_stacks() is called ;
* add a comment to all the functions that pp_return() tail-calls to the
  effect that they can be tail-called;
* make it clearer when/why OPf_SPECIAL is set on OP_LEAVE;
* CXt_LOOP_PLAIN can be a while loop as well as a plain block.

1 files changed, 2 insertions, 1 deletions

diff --git a/op.h b/op.h
index 00d9a4c88f..3ded4bb318 100644
--- a/op.h
+++ b/op.h
@@ -113,7 +113,8 @@ Deprecated.  Use C<GIMME_V> instead.
 				/*  On local LVAL, don't init local value. */
 				/*  On OP_SORT, subroutine is inlined. */
 				/*  On OP_NOT, inversion was implicit. */
-				/*  On OP_LEAVE, don't restore curpm. */
+				/*  On OP_LEAVE, don't restore curpm, e.g.
+                                 *      /(...)/ while ...>;  */
 				/*  On truncate, we truncate filehandle */
 				/*  On control verbs, we saw no label */
 				/*  On flipflop, we saw ... instead of .. */