exists function improved

adding a limit(1) is usefull for control of existence and can be find it 1 step in db.
Update QueryBuilder test per changes to exists()
Merge pull request #1 from lol768/patch-2

Update QueryBuilder test per changes to exists()
Merge branch 'patch-1' of https://github.com/irfanevrens/framework into irfanevrens-patch-1
Fix code to not be a breaking chage.