[FIX github issue #1] User is unable to download file with dot in filename

Users were unable to download files with dots in filenames, ie foo.bar.txt
 would match to :file_name => "foo", :format => "bar.txt". This was caused
 by default rails routing policy where dot separates :format part of the
 route match.

The bug is fixed by applying very loose constraints on :file_name matcher 
(anything except slash), making it "hungrier" than :format. Any surplus dots
will be "eaten" by the :file_name, making the correct match, ie
:file_name => "foo.bar", :format => "txt".