tests/failfilemerge.py

formatter: make labels work with templated output

To describe the bug this fix is addressing, one can do
   ``$ hg status -T "{label('red', path)}\n" --color=debug``
and observe that the label is not applied before my fix and applied with it.

# extension to emulate interupting filemerge._filemerge

from __future__ import absolute_import

from mercurial import (
    filemerge,
    extensions,
    error,
)

def failfilemerge(filemergefn,
        premerge, repo, mynode, orig, fcd, fco, fca, labels=None):
    raise error.Abort("^C")
    return filemergefn(premerge, repo, mynode, orig, fcd, fco, fca, labels)

def extsetup(ui):
    extensions.wrapfunction(filemerge, '_filemerge',
                            failfilemerge)