git-p4: chdir now properly sets PWD environment variable in msysGit

P4 on Windows expects the PWD environment variable to be set to the
current working dir, but os.chdir in python doesn't do so.

Signed-off-by: Robert Blum <rob.blum@gmail.com>
Acked-by: Simon Hausmann <simon@lst.de>
Acked-by: Han-Wen Nienhuys <hanwen@xs4all.nl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/fast-import/git-p4

@@ -16,6 +16,11 @@ from sets import Set;
 
 verbose = False
 
+def chdir(dir):
+    if os.name == 'nt':
+        os.environ['PWD']=dir
+    os.chdir(dir)
+
 def die(msg):
     if verbose:
         raise Exception(msg)
@@ -712,7 +717,7 @@ class P4Submit(Command):
         print "Perforce checkout for depot path %s located at %s" % (self.depotPath, self.clientPath)
         self.oldWorkingDirectory = os.getcwd()
 
-        os.chdir(self.clientPath)
+        chdir(self.clientPath)
         print "Syncronizing p4 checkout..."
         system("p4 sync ...")
 
@@ -732,7 +737,7 @@ class P4Submit(Command):
 
         if len(commits) == 0:
             print "All changes applied!"
-            os.chdir(self.oldWorkingDirectory)
+            chdir(self.oldWorkingDirectory)
 
             sync = P4Sync()
             sync.run([])
@@ -1670,7 +1675,7 @@ class P4Clone(P4Sync):
         print "Importing from %s into %s" % (', '.join(depotPaths), self.cloneDestination)
         if not os.path.exists(self.cloneDestination):
             os.makedirs(self.cloneDestination)
-        os.chdir(self.cloneDestination)
+        chdir(self.cloneDestination)
         system("git init")
         self.gitdir = os.getcwd() + "/.git"
         if not P4Sync.run(self, depotPaths):
@@ -1782,7 +1787,7 @@ def main():
                 if os.path.exists(cmd.gitdir):
                     cdup = read_pipe("git rev-parse --show-cdup").strip()
                     if len(cdup) > 0:
-                        os.chdir(cdup);
+                        chdir(cdup);
 
         if not isValidGitDir(cmd.gitdir):
             if isValidGitDir(cmd.gitdir + "/.git"):