Normalizing image url for UrlStorage

Added url sanitation to prevent error "HTTP Error 505: HTTP Version Not Supported".

* Added utf8 encode to "path"
Added comments
Added check if path is unicode
Tests for normalizing UrlStorage url to prevent 505 HTTP errors #200
Merge branch 'master' of github.com:mariocesar/sorl-thumbnail

* 'master' of github.com:mariocesar/sorl-thumbnail:
  Always use compat.BufferIO in pil_engine.