SMP - Breaking Blocks on Laggy Server is Buggy

With the change that causes block breaking to reset when you change tools, there is an annoying side effect on laggy servers. If there is a delay between the time when you break a block, and the block actually "pops", when the block actually breaks, if you were in the middle of breaking a second block, the block breaking on the second block resets.

How to reproduce:
1. Login to a server that has a little lag.
2. Break a block.
3. Immediately start breaking a second block.
4. When the first block "pops", your second block breaking will reset.

This is annoying especially when you have a decently fast pick, because you have to "break" every block twice before they actually break.