Add -dbstats argument.

Implement the -dbstats argument, which runs a database file storage
statistics analysis and prints it to the debug log.
Merge pull request #85 from domob1812/remove-vspent

Further update blkindex.dat by changing the vSpent format
Merge pull request #89 from domob1812/analyse-db

Add -dbstats argument from Huntercoin to analyse BDB storage