A Code ID is computed as an MD5 checksum over the actual code, as an
byte[] array.  (Called a MethodID or mid in the code, probably should
be called a 'CapsuleID'.)

A Group ID is computed by taking the (capsule) code ids, sorting them,
and computing an MD5 checksum over it.

A ProtocolID is computed by taking the (code) group ids, sorting them,
and computing an MD5 checksum over it.

Note: A protocol ID can be computed even if only one code group was
transmitted (using DLResponse/DLRequest) because any DLResponseCapsule
contains *all* GroupIDs for the Protocol!

A Method ID is computed by sending a Code ID, its Group ID, and its
Protocol ID through MD5, in that order.  Thus, a method ID describes
a triple (Capsule_i, Code Group_j, Protocol_k).

NOTE: It is the Method ID that is sent in the header of a capsule.
    It is hence the basis for demultiplexing.



---------------
Format of DLRequest:

offset	len	type
0	16	TypeID		Code ID that I want code for
16	 4	int		bit vector for parts of CodeGroup that
				I don't have already

--------------
Format of DLResponse:
offset 	len	type
0	16	TypeID		Code ID of contained code chunk
16	16	TypeID		CodeGroup ID
32	 2	short		# l = of groups in the protocol
34	16*l	TypeID[]	code group id of other "groups" in the protocol
	 4	int		"part"th code part this capsule includes
	 4	int		"clen" -- total length of code
	 ?	String		_cn - Name of capsule class
	 ?	ByteArray	chunk of byte code

--------------

Activities performed by DLThread

- unknown capsule received
	- create DLBootstrap
		- first time? -> make entry in code cache
		- create and send DLRequest

- DLRequest capsule received - service for other nodes

- DLResponse capsule received
	- find target method
	- retrieve or, if necessary, create code group 
	- add method to group
	- allocate byte array for code the first time
	- copy code part into code
	- if all done, activate code group
		- compute code ids
		- compute protocol id