Improve file naming with phpthumof.hash_thumbnail_names off

Fixes two problems:
1. Gives different names to files in different directories which happen
to have the same name, phpthumb options and be called from the same
resource.
2. Doesn't give a diffenent name to the same file with the same options
when it's called from different resources.
Naming improvements for cache files; disable cache cleanup for better performance
Revert "Naming improvements for cache files; disable cache cleanup for better performance"

This reverts commit af410a915425e647733baccec4a4ba12720845a9.
Merge remote-tracking branch 'splittingred/pr/49' into pr-49