tests/failfilemerge.py

fsmonitor: add new watchman notifications to fsmonitor extension

The fsmonitor extension currently sends state-enter and state-leave
notifications to watchman on the update operation. This commit creates
additional notifications for the following events :

- transaction creation and commit/abort. A state-enter notification will be
  sent when a transaction is created.  It will provide the working copy
  parent's hash. A state-leave notification will be sent when the
  transaction is committed or aborted. It will provide the working copy
  parent's hash.
- calls to set-parent will cause state-enter and state-leave notifications
  to be sent. The state-enter notification will be sent prior to the
  set-parent operation and the working copy parent's hash will be provided at
  this time. The state-leave notification will be sent after the set-parent
  operation completes providing the working copy parents hash.

Test Plan:
tested on dev server to check that necessary notifications were sent/received

Differential Revision: https://phab.mercurial-scm.org/D989

# extension to emulate interrupting filemerge._filemerge

from __future__ import absolute_import

from mercurial import (
    error,
    extensions,
    filemerge,
)

def failfilemerge(filemergefn,
                  premerge, repo, wctx, 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)