[android] a guess of the MIME type is added to the Intent when opening a file:///... URL

I used to have errors like the one mentioned in https://groups.google.com/forum/?hl=en#!searchin/phonegap/inappbrowser/phonegap/pgBYjpSmHU4/i_O2jUQnowkJ . This fix solved the problem in my case; I'm not sure whether it is generic enough though.