Bug fixes & new tests for Lucene Directory v3 & v4

I've fixed the bug:

ISPN-2789 - OutOfMemoryError in case if LuceneCacheLoader.loadAll() is called
   - The bug is fixed, new tests are added covering both the bug case as well as adding code coverage to the module;

ISPN-2788 - NullPointerException appears in case passing null as an exclusion list to LuceneCacheLoader.loadAllKeys() 
   - The bug has been fixed. But one of my tests caught another appearance of the bug. This commit contains the fix for the bug as well as the new test verifying that it is complete.

The new code is tested and works properly. No test failures occur.