Bugs fixed:
  - Use randomly generated flags as the spec required.
  - During envelope opening check the first bit only for signature.

xeth: fix #640, panic converting nil recipient to hex.

Fetching the recipient address from a transaction was changed to return nil
instead of a zero-address, but this code path was not updated, so whenever
a contract was created, a nil panic occured.

bugfix as a result of PR 671

@zelig: Temporarily commented out TD check untill the rest of the network has
been fixed.