Remove an unneccessry check that prevented some assets from being imported properly

Importing assets relative to a file bing imported by another file (when
the relative location was not the same as for the original importing
file) didn't work as it does in sass-rails.  Added a test to catch this
case and removed an unneccessary check that was causing the error.
Merge pull request #23 from wadetandy/master

Remove an unneccessry check that prevented some assets from being imported properly