Fix problem with accepting tx to mempool.

The update to 1.0.13 introduced an issue where transactions spending
unconfirmed outputs were not allowed into the mempool.  This is fixed
now.
Merge pull request #87 from domob1812/fix-pending

Fix problem with accepting tx to mempool.
Use UTXO db to cross-check priority calculation.

Use the UTXO database to look up previous transactions in CreateNewBlock
and compare the resulting data for a tx's priority to the old
calculation.  This is a first step in removing the load from the
blockchain itself and replacing it with *only* the UTXO lookup.
Use only UTXO set to calculate transaction priorities.
Simplify name_show and name_history.

Simplify the implementations of name_show and name_history.  This makes
it possible to get rid of GetValueOfTxPos and some redundant disk loads.
Remove now unused GetNameAddress(CDiskTxPos).
Remove obsolete FIXME remark.
Replace ReadTxIndex by ContainsTx in wallet.cpp.

Replace a call to ReadTxIndex by the "simpler" ContainsTx at one place
where this is all that is actually used.
Remove FetchInputs.

Remove FetchInputs and manually code some logic in signrawtranscation.
The new logic tries to load the tx from the wallet, mapTransactions or
the UTXO set.  No access to the blockchain itself is tried.
Replace GetTransaction by mapTransactions in name_pending.
Merge pull request #82 from domob1812/priority-calc

Some cleanup of the code.
Implement "new-style" name_firstupdate operations.

After a planned hardfork, allow name_firstupdate operations to take
place without a preceding name_new.  In this case, no hash/rand value is
present, and no checks are done for this.  This will allow simpler name
registrations in the future, at the loss of protection against "name
stealing" -- which seems no big deal in Huntercoin anyway.
Add RPC call for new-style registration.

The new RPC command 'name_register' performs new-style name
registration.  Also fix a problem with mining these.