Add missing main()

Previously, "console_scripts" in "setup.py" was pointing to a
non-existent main().

src/cdiff.py

                 yield line
 
 
-def markup_to_pager(stream):
+def markup_to_pager(stream, opts):
     markup = DiffMarkup(stream)
     color_diff = markup.markup(side_by_side=opts.side_by_side,
             width=opts.width)
         return line
 
 
-if __name__ == '__main__':
+def main():
     import optparse
 
     supported_vcs = [check[0] for check, _ in REVISION_CONTROL]
             sys.stderr.write(('*** Not in a supported workspace, supported '
                               'are: %s\n\n') % ', '.join(supported_vcs))
             parser.print_help()
-            sys.exit(1)
+            return 1
     else:
         diff_hdl = sys.stdin
 
 
     # Don't let empty diff pass thru
     if not stream:
-        sys.exit(0)
+        return 0
 
     if diff_hdl is not sys.stdin:
         diff_hdl.close()
 
     if sys.stdout.isatty():
         try:
-            markup_to_pager(stream)
+            markup_to_pager(stream, opts)
         except IOError:
             e = sys.exc_info()[1]
             if e.errno == errno.EPIPE:
         # pipe out stream untouched to make sure it is still a patch
         sys.stdout.write(''.join(stream))
 
-    sys.exit(0)
+
+if __name__ == '__main__':
+    sys.exit(main())
 
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