Timezone compatibility fix, progressive jpeg support

First off, thanks for writing this library and making it available...super helpful.

Second, I haven't tested either of these commits extensively so feel free to ignore this pull request altogether. 

This fixes two issues that made the library incompatible with my Django installation (timezone support and progressive jpeg loading). The fix for the progressive jpeg loading is based on this stackoverflow response: http://stackoverflow.com/a/6789306/260722.