color: add effect to the template symbol table

Previously, words like 'red' had to be protected by quotes before passing to
the label template function. Now, we add color effects to the symbol table so
that commands like,

$ hg log -r . -T "{label(red, node|short)}\n"

can work without the need for quoting.

hgext/color.py

@@ -395,6 +395,10 b' def templatelabel(context, mapping, args'
         # i18n: "label" is a keyword
         raise error.ParseError(_("label expects two arguments"))
 
+    # add known effects to the mapping so symbols like 'red', 'bold',
+    # etc. don't need to be quoted
+    mapping.update(dict([(k, k) for k in _effects]))
+
     thing = templater._evalifliteral(args[1], context, mapping)
 
     # apparently, repo could be a string that is the favicon?