Ban improperly created burn address, various other improvements for 1.1 release

Full list of improvements for 1.1 release:

* Burn address created by ccex has been banned, ensuring that these funds are actually unspenable
* Time drift allowance has been reduced from 1 day to 1 hour
* Leveldb has been replaced so that it no longer gives compiler errors
* Checkpoint has been added
* Added 2 DNS seeds so that addnode in configuration files should in theory be optional
* Directory structure fleshed out so `make -f makefile.unix` just works, without any extra steps