Document return value of VALGRIND_MAKE_MEM_DEFINED and friends.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14089 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/memcheck/docs/mc-manual.xml b/memcheck/docs/mc-manual.xml
index a2a2e09..1745d7a 100644
--- a/memcheck/docs/mc-manual.xml
+++ b/memcheck/docs/mc-manual.xml
@@ -1930,7 +1930,8 @@
     <varname>VALGRIND_MAKE_MEM_DEFINED</varname>.
     These mark address ranges as completely inaccessible,
     accessible but containing undefined data, and accessible and
-    containing defined data, respectively.</para>
+    containing defined data, respectively. They return -1, when
+    run on Valgrind and 0 otherwise.</para>
   </listitem>
 
   <listitem>