add support for local files

add support for local files #45

removing the check for null content-type allows highlighting on local files.  a quick test shows this works for local files and retains functionality for hosted files.  before this gets merged I would like to know why the check was in there, maybe there is some history I am missing.

![image](https://f.cloud.github.com/assets/166513/2387576/67fdac72-a938-11e3-9835-7bd02bb806e1.png)