Add game_getpath RPC command.

Create a new RPC command game_getpath that makes the internal shortest
path algorithm accessible to front-ends.
Merge pull request #43 from domob1812/rpc-waypoints

Add game_getpath RPC command.
Make CTxIndex::vSpent private.

Make the CTxIndex::vSpent member private, and access it only via
interface functions from the outside.
Fix vSpent private merge.

Fix remaining usings of CTxIndex::vSpent in Huntercoin-specific code.
This requires adding an accessor to vSpent with disk position, to check
if the spending tx is a game tx.  This can be removed later on, though,
to allow for the actual optimisations.
Change internal vSpent data format.

Actually change the vSpent array internally to be an array of flags
instead of full tx positions.  Not yet efficiently as a bit vector,
though.
Fully rewrite txindex on upgrading blkindex.dat format.

When upgrading the blkindex.dat data format, actually fully rewrite the
txindex objects stored in it.
Fix merge from Namecoin.

Replace the version number used in the patch from Namecoin to the
correct one for Huntercoin.
Add progress print-outs to tx rewriting.
Implement tx upgrading more efficient.

Do the tx database upgrade more efficiently.  Instead of randomly
loading all spending tx's, go through the blockchain in an ordered
fashion instead.
Add progress indicator to tx index rewriting.