Made sure that DRD processes empty address ranges without triggering an assertion failure. Added a unit test in drd/tests/unit_bitmap.c.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11346 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/drd/drd_clientobj.c b/drd/drd_clientobj.c
index 780b793..e3b6a94 100644
--- a/drd/drd_clientobj.c
+++ b/drd/drd_clientobj.c
@@ -107,7 +107,7 @@
 {
    DrdClientobj *p;
 
-   tl_assert(a1 < a2);
+   tl_assert(a1 <= a2);
    VG_(OSetGen_ResetIter)(s_clientobj_set);
    for ( ; (p = VG_(OSetGen_Next)(s_clientobj_set)) != 0; )
    {