Sass watcher should prioritize cwd when resolving @imports.

[xzyfer]

Originally mentioned xzyfer/sass-graph#12

When a save event happens we inspect the import graph to determine the least amount of files that need compiling. This results in almost instant compilations on saves.

Currently however when walking the import graph we do not respect the behaviour of checking the current working directory first. This can result in the wrong files being compiled if there are naming collisions.