A new version of fsmonitor-watchman hook has been introduced, to
avoid races.
* kw/fsmonitor-watchman-racefix:
fsmonitor: update documentation for hook version and watchman hooks
fsmonitor: add fsmonitor hook scripts for version 2
fsmonitor: handle version 2 of the hooks that will use opaque token
fsmonitor: change last update timestamp on the index_state to opaque token