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/main.py b/main.py
index 278fd36..d993ee4 100755
--- a/main.py
+++ b/main.py
@@ -146,13 +146,13 @@
           else:
             print >>sys.stderr, 'real\t%dh%dm%.3fs' \
               % (hours, minutes, seconds)
-    except DownloadError, e:
+    except DownloadError as e:
       print >>sys.stderr, 'error: %s' % str(e)
       return 1
-    except ManifestInvalidRevisionError, e:
+    except ManifestInvalidRevisionError as e:
       print >>sys.stderr, 'error: %s' % str(e)
       return 1
-    except NoSuchProjectError, e:
+    except NoSuchProjectError as e:
       if e.name:
         print >>sys.stderr, 'error: project %s not found' % e.name
       else:
@@ -390,14 +390,14 @@
       close_ssh()
   except KeyboardInterrupt:
     result = 1
-  except RepoChangedException, rce:
+  except RepoChangedException as rce:
     # If repo changed, re-exec ourselves.
     #
     argv = list(sys.argv)
     argv.extend(rce.extra_args)
     try:
       os.execv(__file__, argv)
-    except OSError, e:
+    except OSError as e:
       print >>sys.stderr, 'fatal: cannot restart repo after upgrade'
       print >>sys.stderr, 'fatal: %s' % e
       result = 128