Improve suppression matching performance when fun or obj is a simple string

Improve suppression matching performance when fun or obj is a simple string
Idea is from Julian, possible bugs are mine.

If the fun or obj is a simple string and not a patter (so no *, no ?),
use a simple string comparison rather than a call to a wildcard matching.

On a leak search with a lot of reachable loss records and a lot of suppr,
it improves the speed of the leak search by 10 to 15%.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12789