Use iterables to determine the best filename to use for changes.

setup.py

@@ -90,12 +90,12 @@ class test(_test):
 
 readme_file = io.open('README.txt', encoding='utf-8')
 
-# the release script adds hyperlinks to issues
-if os.path.exists('CHANGES (links).txt'):
-    changes_file = io.open('CHANGES (links).txt', encoding='utf-8')
-else:
-    # but if the release script has not run, fall back to the source file
-    changes_file = io.open('CHANGES.txt', encoding='utf-8')
+# The release script adds hyperlinks to issues,
+# but if the release script has not run, fall back to the source file
+changes_names = 'CHANGES (links).txt', 'CHANGES.txt'
+changes_fn = next(filter(os.path.exists, changes_names))
+changes_file = io.open(changes_fn, encoding='utf-8')
+
 with readme_file:
     with changes_file:
         long_description = readme_file.read() + '\n' + changes_file.read()