fix test and add one for LoaderTask similar to ImageManagerTest
fix LoaderTask on failed decoding
even delete corrupted files
extract logic for image loading into BitmapRetriever, should be reused in SimpleLoader as well.
use BitmapRetriever in SimpleLoader
define CacheManager.remove and implement it, add tests
use new cachemanager API in bitmap retriever test
Increments to 1.6.1 due to cacheManager api change
Merge pull request #142 from novoda/more_tests

fix test and add one for LoaderTask similar to ImageManagerTest