Update release notes script to ignore merges.

Author: damonkohler

tools/release_notes.py

@@ -6,4 +6,6 @@
 repo = hg.repository(ui.ui(), '..')
 changes = [d for d in repo[sys.argv[1]].descendants()]
 for c in changes:
-  print c.description()
+  description = c.description()
+  if description != 'merge' and description != 'Merge':
+    print description