callgrind_control: fix parsing of vgdb -l

callgrind_control: fix parsing of vgdb -l

If valgrind is called with absolute path (as qtcreator does),
callgrind_control found nothing, as it looked for
"... for valgrind ...", thus breaking qtcreator.

This also fixes expected behavior with client commands called with
absolute path. For "/usr/bin/valgrind --tool callgrind /usr/bin/foo",
running "callgrind_control foo" should catch this callgrind command.
Instead, you previously had to include the absolute path.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11905