Provide several modifications on the PredisStore implementation.
 - Fixed some typos
 - Fixed the way an association is retreived from the store (getAssociation()).
   The existing implementation was poping (LPOP) from a list, causing unneeded
   re-associations. If we need to discard stale association handles, i think we
   should rather set the appropriate expiry intervals.
Merge pull request #121 from drmalex07/master

Provide several modifications on the PredisStore implementation.