swapping the roles of the VALGRIND_DO_CLIENT_REQUEST() and
VALGRIND_DO_CLIENT_REQUEST_EXPR() macros. Also, many __attribute__((unused))
declarations on variables have been eliminated. Closes#269778.
Note: so far this patch has been tested on x86/Linux, amd64/Linux and
ppc64/Linux but not yet on any other supported CPU/OS combination.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11755