Update CHANGES.rst and fix Python 2.6 compat.

Update CHANGES.rst with the RB ID.
Fixup string formatting to be python2.6 compatible.

CHANGES.rst

@@ -7,7 +7,7 @@ CHANGES
 ----------
 
 * Bug fix: Honor installed sys.excepthook in pex teardown.
-  `RB #XXX <https://rbcommons.com/s/twitter/r/XXX>`_
+  `RB #1733 <https://rbcommons.com/s/twitter/r/1733>`_
 
 -----
 0.8.5

tests/test_pex.py

@@ -24,7 +24,7 @@ def test_excepthook_honored():
   import sys
 
   def excepthook(ex_type, ex, tb):
-    print('Custom hook called with: {}'.format(ex))
+    print('Custom hook called with: {0}'.format(ex))
     sys.exit(42)
 
   sys.excepthook = excepthook