Add support for EXT filesystem

This commit should be viewed as a temp hack enabling users of ext
formated external sdcards to use these cards with cyanogenmod9.
I've taken and applied two commits from branch gingerbread enabling
ext support in vold by hacking fat.cpp. I would love to backport vold
from branch jellybean but failed on that. Used commit were
3f7120aaebde30375c7115aac0c0f34665697135 and
d0087cca1762887ea8de6c25df58a85075cd1ffc .

Change-Id: I677a165c8df2761e24db02654d9893a092cf45a3