Use modern Python exception syntax

"except Exception as e" instead of "except Exception, e"

This is part of a transition to supporting Python 3.  Python >= 2.6
support "as" syntax.

Note: this removes Python 2.5 support.

Change-Id: I309599f3981bba2b46111c43102bee38ff132803
diff --git a/subcmds/init.py b/subcmds/init.py
index 007667e..b6b9807 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -207,7 +207,7 @@
 
     try:
       self.manifest.Link(name)
-    except ManifestParseError, e:
+    except ManifestParseError as e:
       print >>sys.stderr, "fatal: manifest '%s' not available" % name
       print >>sys.stderr, 'fatal: %s' % str(e)
       sys.exit(1)