(facebook) change expire_after to relative time
fix obsolete 'code' handling
Merge branch 'dev' of github.com:hupili/snsapi into dev
Merge remote-tracking branch 'upstream/dev'
code cleaning and set defaults:

   * original FB does not support two-stage async auth.
   Now it supports, we revert to SNSAPI default.
   See 'snstype.AuthInfo' for the defaults.
resolved