Honor url.insteadOf when setting up SSH control master connection

Repo can now properly handle url.insteadOf sections in the
user's ~/.gitconfig file.  This means that a user can now enjoy
the master-ssh functionality even if he/she uses insteadOf's in
~/.gitconfig to rewrite git:// URLs to ssh:// style URLs.

Change-Id: Ic0f04a9c57206a7b89eb0f10bf188c4c483debe3
Signed-off-by: Shawn O. Pearce <sop@google.com>

git_config.py

diff --git a/git_config.py b/git_config.py
index e1e2046..45a2d25 100644
--- a/git_config.py
+++ b/git_config.py
@@ -442,8 +442,30 @@
                      self._Get('fetch', all=True))
     self._review_protocol = None
 
+  def _InsteadOf(self):
+    globCfg = GitConfig.ForUser()
+    urlList = globCfg.GetSubSections('url')
+    longest = ""
+    longestUrl = ""
+
+    for url in urlList:
+      key = "url." + url + ".insteadOf"
+      insteadOfList = globCfg.GetString(key, all=True)
+
+      for insteadOf in insteadOfList:
+        if self.url.startswith(insteadOf) \
+        and len(insteadOf) > len(longest):
+          longest = insteadOf
+          longestUrl = url
+
+    if len(longest) == 0:
+      return self.url
+
+    return self.url.replace(longest, longestUrl, 1)
+
   def PreConnectFetch(self):
-    return _preconnect(self.url)
+    connectionUrl = self._InsteadOf()
+    return _preconnect(connectionUrl)
 
   @property
   def ReviewProtocol(self):