#4482 - Array to string conversion in deep Arr::merge

When using Arr::merge to merge arrays, the deeper array merges failed
and caused a ErrorException [ Notice ]: Array to string conversion

See: http://dev.kohanaframework.org/issues/4482
Added strict in in_array

Added extra entry to array in test and changed in_array to strict.
Performance:
Non Strinct: http://i.imgur.com/JiRtUxQ.png
Strict: http://i.imgur.com/nRmgHVS.png
Merge pull request #428 from JackEllis/bugfix-4482

#4482 - Array to string conversion in deep Arr::merge