Support spaces in GREP pattern for make test
IndexingTestDb: cleaner error propagation in readFromIndex

This should not matter with the mock store, but just to be sure.
IndexMixin: add method removeIndex

This should be available so that a collection user can remove only
the index while leaving the models intact.
Merge pull request #17 from Everyplay/feature/remove-index

Add method removeIndex to IndexMixin