Issue #1706706 by girishmuraly, melon, catch: Fixed files should be rebuilt upon drupal_flush_all_caches().

Revert "Issue #1459526 by msonnabaum: Fixed Prevent duplicate files as arrays due to race conditions."

This reverts commit 8b44525a.

#1040492: by justinrandell, catch: Use raw file contents for filename hash to avoid processing twice.

Ensure that the css map is always added to rather than overwritten when multiple threads are trying to build the array at the same time.