Fixes invalidating image within cache when image is nil.
Renames and improves added test.
removeAllImages doesn't rebuild disk cache

Calling removeAllImages on HNKCache causes each format to delete its
disk cache directory permanently, leading to cache write errors
following the call.

The solution is for a format to rebuild its cache directory after
removing it.
Merge pull request #42 from julianhirt/FixesResettingImageForKey

Fixes invalidating image within cache when image is nil.
Merge pull request #43 from blushmessenger/master

removeAllImages doesn't rebuild disk cache
Add unit test for bug #43
Remove disk cache contents one by one instead of removing and recreating the directory
Increase version
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Increase version
  Remove disk cache contents one by one instead of removing and recreating the directory
  Add unit test for bug #43
  removeAllImages doesn't rebuild disk cache
  Renames and improves added test.
  Fixes invalidating image within cache when image is nil.