Made getKeys return a unique array of keys.

This was causing applications to crash if there was somehow thousands of keys, but where most the same.

Caused the program to error with a status code of 100. With no errors at all.

This is hard to replicate, but with eager loading and belongsToMany relations, this bug was happening.

[EDIT] I've done a little more searching and this was causing PHP to crash causing a Apache "Segmentation fault (11)" and killing off a child.