Make freenect_flags an actual flag enum

Signed-off-by: Robert Xiao <brx@cs.cmu.edu>
Merge pull request #342 from nneonneo/freenect-flag-fix

freenect_flag should be a real flags enum (raw registers should be coded differently) (@nneonneo)

Reviewed-by: Benn Snyder <benn.snyder@gmail.com>