get_maintainers.pl: follow renames when looking up commit signers

I happen to have had a commit to various network drivers since the big
renaming/reorg which happened to drivers/net recently.  This means that I
now appear to be in the top few commit signers (by %age) for many of them
so am getting sent all sorts of stuff and people who are involved with the
driver are not.  e.g.  (to pick one at random):

        $ ./scripts/get_maintainer.pl -f drivers/net/ethernet/nvidia/forcedeth.c
        "David S. Miller" <[email protected]> (commit_signer:5/7=71%)
        Ian Campbell <[email protected]> (commit_signer:2/7=29%)
        Eric Dumazet <[email protected]> (commit_signer:1/7=14%)
        Jeff Kirsher <[email protected]> (commit_signer:1/7=14%)
        Jiri Pirko <[email protected]> (commit_signer:1/7=14%)
        [email protected] (open list:NETWORKING DRIVERS)
        [email protected] (open list)

With the following patch the renames are followed and the result appears
much more sensible:

        $ ./scripts/get_maintainer.pl -f drivers/net/ethernet/nvidia/forcedeth.c
        "David S. Miller" <[email protected]> (commit_signer:31/34=91%)
        Joe Perches <[email protected]> (commit_signer:11/34=32%)
        Szymon Janc <[email protected]> (commit_signer:5/34=15%)
        Jiri Pirko <[email protected]> (commit_signer:3/34=9%)
        Paul <[email protected]> (commit_signer:2/34=6%)
        [email protected] (open list:NETWORKING DRIVERS)
        [email protected] (open list)

Signed-off-by: Ian Campbell <[email protected]>
Acked-by: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/get_maintainer.pl

@@ -95,7 +95,7 @@
     "execute_cmd" => \&git_execute_cmd,
     "available" => '(which("git") ne "") && (-d ".git")',
     "find_signers_cmd" =>
-	"git log --no-color --since=\$email_git_since " .
+	"git log --no-color --follow --since=\$email_git_since " .
 	    '--format="GitCommit: %H%n' .
 		      'GitAuthor: %an <%ae>%n' .
 		      'GitDate: %aD%n' .