tried to merge in sipa's watch-only patch

Conflicts:
	src/rpcserver.cpp
qt: Hide unspendable outputs in coin control
Watchonly balances are shown separately in gui.
Watchonly transactions are marked in transaction history
added watchonly parameter to getbalance and fixed errors in balance calculation.
added watchonly parameter to listaccounts
added watchonly parameter to listtransactions and listsinceblock
Showing 'involvesWatchonly' property for transactions returned by 'listtransactions' and 'listsinceblock'.
It is only appended when the transaction involves a watchonly address.