color: colorize based on output labels instead of parsing output
By overriding ui.write(), ui.write_err(), ui.popbuffer(), and ui.label(),
the color extension can avoid parsing command output and simply colorize
output based on labels.
As before, the color extension provides a list of default colors for
core commands/labels. Other extensions can provide their own defaults by
specifying a colortable dict (similar to cmdtable).
In this process, --color is promoted to a global option and the deprecated
--no-color option is removed.
% reverting to rev 0
reverting foo
M foo
diff --git a/foo b/foo
old mode 100755
new mode 100644