Add an alert for python < 2.5.

Don't block execution.

Python 2.4 has been untested for a while and may break unexpectedly.

TEST=manual testing
BUG=none

Review URL: http://codereview.chromium.org/5110009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@66870 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/gclient.py b/gclient.py
index 6817db1..98a8192 100644
--- a/gclient.py
+++ b/gclient.py
@@ -1193,6 +1193,9 @@
 def Main(argv):
   """Doesn't parse the arguments here, just find the right subcommand to
   execute."""
+  if sys.hexversion < 0x02050000:
+    print >> sys.stderr, (
+        '\nYour python version is unsupported, please upgrade.\n')
   try:
     # Make stdout auto-flush so buildbot doesn't kill us during lengthy
     # operations. Python as a strong tendency to buffer sys.stdout.