Utils, Mime: Extract mimes-to-extensions mapping logic into a separate method - mimes2exts().
FileDrop, HTML5: Filter drag-n-dropped files by extensions instead of mimes.

Since internal list of mime types is limited, filtering by them gets
too confusing to be useful.
FileInput: Ignore empty files.

IE10 hangs if you try to send them via XHR in HTML5 runtime.
Potentially there might be some other problems as well. Not ignoring
them is not that useful anyway.
JavaScript: Update binaries.