get_maintainer.pl: allow "K:" pattern tests to match non-patch text

Extend the usage of the K section in the MAINTAINERS file to support
matching regular expressions to any arbitrary text that may precede the
patch itself.  For example, the commit message or mail headers generated
by git-format-patch.

Signed-off-by: Joe Perches <joe@perches.com>
Original-patch-by: L. Alberto Giménez <agimenez@sysvalve.es>
Acked-by: L. Alberto Giménez <agimenez@sysvalve.es>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>