Update glob and follow symlinks when looking for partials

Currently, partials don't follow symbolic links.

A common use case (and one we're using) is registering './bower_components' as a partials dir - which works fine - but then trying to use `bower link` (which creates a symbolic link to a local copy of the component repo) to develop locally between components.
Looking at Glob's options it says:

>  A cache of known symbolic links. You may pass in a previously generated symlinks object to save lstat calls when resolving ** matches.

So I'm not sure how passing a value of `true` would have any affect on Glob and make it follow symlinks. Can you explain more how this changes the behavior of Glob?