Fixes #358 - unable to edit '*.html' files in File Manager

Problem: Unable to edit files ending with `.html` extension in File Manager

Reason: Wolf at the very beginning of request processing strips URL_SUFFIX from requests.

Proposed workaround: For files ending with URL_SUFFIX - add `has_url_suffix=1` to query string and detect it's presence while viewing/editing those files.

Not very pretty but works for both `USE_MOD_REWRITE=true` and `false`