Use graceful-fs instead of fs

[steelbrain]

The latest release uses fs.watch from fs instead of the graceful-fs module, which in turn results in this in our app

[steelbrain]

Blocked on isaacs/node-graceful-fs#106

[paulmillr]

we're not going to switch to graceful. It's up to user.

[steelbrain]

@paulmillr I am not really sure how a user could switch to graceful inside of a module that has hardcoded references to the native fs.watch. Could you please elaborate on that?

[paulmillr]

var realFs = require('fs')
var gracefulFs = require('graceful-fs')
gracefulFs.gracefulify(realFs)
require('chokidar')

[steelbrain]

That is not an idea solution but could work. Thanks @paulmillr

[wmertens]

@paulmillr monkey-patching fs is not that great - would you accept a PR that lets the user provide an optional fs module, stored on the FSWatcher class?