Error more pleasantly when trying to use python2.4

(Bitbake rev: 57402ee727c8c1d8f5017534fb0f5e0b20aaaa5b)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/bin/bitbake

@@ -209,6 +209,7 @@ Default BBFILES are the .bb files in the current directory.""")
     else:
         ui = "knotty"
 
+    try:
         try:
             # Dynamically load the UI based on the ui name. Although we
             # suggest a fixed set this allows you to have flexibility in which