Improved getblocks logging.
No need to report block hash as block height is shown and hash can be derived from that.
Display in status bar when a longer invalid chain exists.
Rename, for reasons of least surprise.

Also, reduces confusion when combined with future pull requests.
Show more significant bytes of block hashes.
Fixes Issue #1234 - re-issues getblocks when current node providing them disappears.

Conflicts:

	src/net.cpp

Conflicts:

	.gitignore
Sometimes nodes send many duplicate blocks. This patch disconnects the peer that's running
behind. This shouldn't happen, but it can and does sometimes, so this code caters for that.

This code also becomes more important as the block download algorithm is changed in future,
such as concurrent block downloads from multiple peers, and retries are sent to other peers
when peers seem unresponsive, only to become responsive again later, by which time
they are sending duplicate blocks.

Conflicts:
	src/main.cpp
break after ProcessMessages() to give other peers a chance.
Implement antisocial feature - just request blocks and ask that transactions info not be sent.