Print an easy-to-understand message in case the client program tries to create more threads than what is currently supported by DRD.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@10593 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/drd/drd_thread.c b/drd/drd_thread.c
index 528b7b3..519efe5 100644
--- a/drd/drd_thread.c
+++ b/drd/drd_thread.c
@@ -195,6 +195,10 @@
       }
    }
 
+   VG_(printf)(
+"\nSorry, but the maximum number of threads supported by DRD has been exceeded."
+"Aborting.\n");
+
    tl_assert(False);
 
    return DRD_INVALID_THREADID;