ui_interface: remove unused NotifyBlocksChanged signal

Conflicts:
	src/main.cpp
	src/qt/clientmodel.cpp
rpc: Compute number of confirmations of a block from block height

Currently this uses a CMerkleTx, but that makes no sense as we
have the CBlockIndex available. As noted by @jgarzik.

Conflicts:
	src/rpcblockchain.cpp
remove useless millisleep

reduces time to service requests improving performance
net: Remove MilliSleep from StopNode

I don't understand why it would be there in the first place. This looks
like voodoo, not programming.

Conflicts:
	src/net.cpp
Shutdown cleanup prep-work

Create a boost::thread_group object at the qt/bitcoind main-loop level
that will hold pointers to all the main-loop threads.

This will replace the vnThreadsRunning[] array.

For testing, ported the BitcoinMiner threads to use its
own boost::thread_group.

Conflicts:
	src/main.cpp