add with_roles helper & return distinct resources without select condition

[hollow]

also fixes some trailing whitespaces and unused variables

[wldcordeiro]

This is an interesting change. I'm going to test it out but just need to get Travis to build properly.

[coveralls]

Coverage increased (+18.53%) when pulling fbb7fe9 on remerge:master into 34e708a on RolifyCommunity:master.

[hollow]

i've rebase this against master. however the mongoid adapter does not return a proper relation object, so distinct() doesn't work. not exactly sure how to solve that

[werleo]

@hollow for mongoid adapter you should call uniq as it returns Array