replace int with size_t in stream methods

Thus the read(...) and write(...) methods of all stream classes now have identical parameter lists.
This will bring these classes one step closer to a common interface.
gui: remove redundant numTransactions tracking

This number was still tracked even though it's shown nowhere in the UI
anymore. It was originally removed because it didn't match the actual number of
records in the view (which contains outputs, not transactions) thus was
confusing people.

Conflicts:
	src/qt/walletmodel.cpp
	src/qt/walletmodel.h
addrman: Do not propagate obviously poor addresses onto the network
Make CScript::clear() release its memory