Fix git try. git_try.py imports git_cl.py without calling its main.

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index c0d9c9403e38d9b2f4dd3f937df87e5f456b41b5..387aa9b01ce4c4fe9143fbcb1469fabba1f03a19 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -311,6 +311,10 @@ def ShortBranchName(branch):
 class Changelist(object):
   def __init__(self, branchref=None):
     # Poke settings so we get the "configure your server" message if necessary.
+    global settings
+    if not settings:
+      # Happens when git_cl.py is used as a utility library.
+      settings = Settings()
     settings.GetDefaultServerUrl()
     self.branchref = branchref
     if self.branchref: