Get some flexibility in the tag type detection

[GoogleCodeExporter]

Currently an internal table helps guessing the type of tag based on its SAK & 
ATS.
But now phones start being able to emulate tags (CyanogenMod, Kitkat,...) while 
SAK & ATS are still not under control, so being different than expected.

How to get more flexibility?

Getting an environment variable to bypass entirely detection and assume that 
we've a tag of the right type requested by the application?

Or instead of guessing the tag from its SAK/ATS, test proactively if the tag is 
of a specific type?

E.g. ASSERT_MIFARE_DESFIRE(tag) would not check a preset flag but would test 
actively if the card is a DESFIRE by sending a GetInfo command.

Original issue reported on code.google.com by yob...@gmail.com on 3 Dec 2013 at 3:23