Rename CHANGES.txt to CHANGES.rst for GitHub rendering

(cherry picked from commit cbc6a42)

Author: mnaberez

CHANGES.txt CHANGES.rstCHANGES.txt renamed to CHANGES.rst

@@ -36,7 +36,7 @@
 here = os.path.abspath(os.path.dirname(__file__))
 try:
     README = open(os.path.join(here, 'README.rst')).read()
-    CHANGES = open(os.path.join(here, 'CHANGES.txt')).read()
+    CHANGES = open(os.path.join(here, 'CHANGES.rst')).read()
 except:
     README = """\
 Supervisor is a client/server system that allows its users to