scripts/get_maintainer.pl: add signatures from Fixes: <badcommit> lines in commit message

A Fixes: lines in a commit message generally indicate that a previous
commit was inadequate for whatever reason.

The signers of the previous inadequate commit should also be cc'd on
this new commit so update get_maintainer to find the old commit and add
the original signers.

Link: http://lkml.kernel.org/r/33605b9fc0e0f711236951ae84185a6218acff4f.camel@perches.com


Signed-off-by: Joe Perches <joe@perches.com>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>