In order to make this happen, kill all remaining trivial uses of
common/{rlp,value}.go. The non-trivial ones have been updated earlier.

Storing a value in LevelDB copies the bytes, modifying the value
afterwards does not affect the content of the database. This commit
ensures that MemDatabase satisfies the same property.

I forgot to update one instance of "go-ethereum" in commit 3f047be5.

All code outside of cmd/ is licensed as LGPL. The headers
now reflect this by calling the whole work "the go-ethereum library".

change order of block insert and update LastBlock

bugfix, wrong hash stored in blockDb

I don't see why we would need two different accessors for a public field.

* Reimplemented caching for trie
* Reimplemented resetting and persisting trie