its beginning or to a given block.  It takes 2 arguments, both of them 256-bit.
The first argument is the account, so its 256-bit public key should be encoded
as binary in big-endian notation.  The second argument is the block hash to
stop sending at, or 256 bits of 0s to indicate that the entire chain should be
sent.  The payload for Bulk_Pull messages is 64 bytes in size.

The response from a Bulk_Pull request will be a stream of tuples, each
containing a 256-bit block hash, and a block message.  TODOC: Format
containing a 8-bit block type identifier, and a block message.  When no more
blocks are available the response is terminated by sending the block type
identifier for
.I not_a_block
and no block message follows.

.TP
.B Bulk_Push
TODOC

.TP
.B Frontier_Req