tests/test-ui-color.py

color: call correct superclass method in write_err

Without this fix, any calls to write_err would go to stdout instead of
stderr, and calls during pushbuffer would cause unpack ValueErrors on
popbuffer.

#!/usr/bin/env python

from hgext import color

# ensure errors aren't buffered
testui = color.colorui()
testui.pushbuffer()
testui.write('buffered\n')
testui.warn('warning\n')
testui.write_err('error\n')
print repr(testui.popbuffer())