Add functionality to get the database backing store and make
sure that we normalize the file paths in the BlockLoader
CON-83: Prevent data duplication during unexpected shutdowns

This commit makes some changes to the server startup logic to
detect cases when there might be duplicate data when the server
restarts after a crash. Duplicate data would occur if the server
crashed after one or more blocks was synced but before the corresponding
buffer page was deleted. The changes contained within try to detect
those possibilities by checking for balanced blocks and also
verifying that transported Writes are acceptable upon initial startup
Use checksums to prevent loading blocks with duplicate data