Changed TxIn.PreviousOutpoint to TxIn.PreviousOutPoint after btcwire API change.
Make use of the new btcchain MedianTimeSource.

This commit uses the new MedianTimeSource API in btcchain to create a
median time source which is stored in the server and is fed time samples
from all remote nodes that are connected.  It also modifies all call sites
which now require the the time source to pass it in.
Update addblock util for recent chain API changes.
Merge branch 'master' into btcdmon