Make it possible to invoke git-p4 from within subdirectories of a git working tree.

Signed-off-by: Simon Hausmann <hausmann@kde.org>
diff --git a/contrib/fast-import/git-p4.py b/contrib/fast-import/git-p4.py
index a075340..f940e93 100755
--- a/contrib/fast-import/git-p4.py
+++ b/contrib/fast-import/git-p4.py
@@ -925,6 +925,10 @@
 gitdir = cmd.gitdir
 if len(gitdir) == 0:
     gitdir = ".git"
+    if not isValidGitDir(gitdir):
+        cdup = os.popen("git-rev-parse --show-cdup").read()[:-1]
+        if isValidGitDir(cdup + "/" + gitdir):
+            os.chdir(cdup)
 
 if not isValidGitDir(gitdir):
     if isValidGitDir(gitdir + "/.git"):