get_maintainer: fix detection of git repository

Since git v1.7.7, the .git directory can be a file when, for example,
the kernel is a submodule of another git super project.  So, the check
"-d .git" is not working anymore in this case.  Using a more generic
check like "-e .git" corrects this behaviour.
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/get_maintainer.pl

@@ -95,7 +95,7 @@ my %VCS_cmds;
 
 my %VCS_cmds_git = (
     "execute_cmd" => \&git_execute_cmd,
-    "available" => '(which("git") ne "") && (-d ".git")',
+    "available" => '(which("git") ne "") && (-e ".git")',
     "find_signers_cmd" =>
 	"git log --no-color --follow --since=\$email_git_since " .
 	    '--numstat --no-merges ' .