Got a LevelDB chain store again

- Using LevelDB in 64-bit mode, FileDB otherwise.
--- This uses a native Windows library that I built from the Bitcoin
source code.
--- Renamed libleveldb.so.1 to leveldb.dll so it works with
leveldb-sharp.
--- Note that you'll have to manually delete all the chain files before
each run, since I still haven't made it possible to pick up the sync
where it left off on a restart.
- Miscellaneous other cleanups.