Merge the DARWIN branch onto the trunk.

I tried using 'svn merge' to do the merge but it did a terrible job and
there were bazillions of conflicts.  So instead I just took the diff between
the branch and trunk  at r10155, applied the diff to the trunk, 'svn add'ed
the added files (no files needed to be 'svn remove'd) and committed.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@10156

memcheck/tests/stack_changes.c

@@ -10,7 +10,7 @@
 // This test is checking the libc context calls (setcontext, etc.) and
 // checks that Valgrind notices their stack changes properly.
 
-#if defined(_AIX)
+#if defined(_AIX) || defined(__APPLE__)
 typedef  ucontext_t  mycontext;
 #else /* linux */
 typedef  struct ucontext  mycontext;