color: add missing 'dim' in _effects

It seems that this has been missing for people running in 'ansi' mode.

hgext/color.py

@@ -156,7 +156,7 b" testedwith = 'internal'"
 # start and stop parameters for effects
 _effects = {'none': 0, 'black': 30, 'red': 31, 'green': 32, 'yellow': 33,
             'blue': 34, 'magenta': 35, 'cyan': 36, 'white': 37, 'bold': 1,
-            'italic': 3, 'underline': 4, 'inverse': 7,
+            'italic': 3, 'underline': 4, 'inverse': 7, 'dim': 2,
             'black_background': 40, 'red_background': 41,
             'green_background': 42, 'yellow_background': 43,
             'blue_background': 44, 'purple_background': 45,