Add support to check if the url has changed for a git dep and create a new clone.

gclient_scm.py

Index: gclient_scm.py
===================================================================
--- gclient_scm.py	(revision 79275)
+++ gclient_scm.py	(working copy)
@@ -186,6 +186,12 @@
       verbose = ['--verbose']
       printed_path = True
 
+    current_url = self._Capture(['config', 'remote.origin.url'])
+    if current_url != url:
+      print('_____ switching %s to a new checkout' % self.relpath)

[M-A Ruel, 2011/03/24 14:49:42]

to a new upstream

+      self._CheckClean(rev_str)

[TVL, 2011/03/24 14:43:19]

actually, this doesn't seem to catch new files.  do we have anything to catch
that?

+      gclient_utils.RemoveDirectory(self.checkout_path)

[M-A Ruel, 2011/03/24 14:49:42]

You don't need to remove the directory at all. Something like that would make
sense:
git remote set-url origin <newurl>
git fetch origin --prune --quiet
# Then forcibly rebase master on the new origin, that needs to be tested.
git reset --hard origin/master

+
     if revision.startswith('refs/heads/'):
       rev_type = "branch"
     elif revision.startswith('origin/'):