Fix opening files from Email app.

On 2.3.x, opening files from the Android email app (not Gmail), was causing
a crash due to a SecurityException. On 4.x, it was failing with an error
message.

I think we should have just been calling
getContentResolver().openInputStream(uri) to get the file data, rather than
reading the row from the content resolver and looking at the _data field.
On 2.3.x querying this row caused a security error. On 4.x, we got back
a _data field containing a path, but this path was internal to the email
app, and not for our consumption.

Previously we were calling openInputStream() only as a fallback; now we try
it first, and fall back to the other method if that fails. I suspect we can
delete the other code, but I can't test on the 3.x version of the Transformer
Prime, so I'm leaving it be for now.
Pass mimetype when opening a document from a stream.

Fixes opening non-PDF files from email programs that use a ContentProvider
to supply attachments.
Handle the application/xps mimetype.

I think this is non-standard, but some applications seem to use it.

The email app on Android uses it, despite the fact the original email
actually embedded it as application/octet-stream. I guess the email app
is looking at the filename.