these functions must usually only be called once this is all done via
a mutex protected list.

common to all server implementations.

Add hard-coded prototypes for functions that return function pointers for
each specific server implementation.

code which given a protocol, e.g. "das", will load the DAS routine function
pointers and call them. These pointers are set up once per protocol and
then reused for each subsequent connection to a server of this protocol.

have such routines and they really must only be called once. This routine
also returns a void* which actually contains the function pointers for the
specific server routines.

Add a length to the request routine, we can't assume C strings will be
returned.

Change code that creates a ZMap to use new ZMap calls that do this.
Add code to load data into a zmap and also to reset one, the latter
operation is unfinished.

Sort out the killing of GUI and threads so they are correct for a ZMap
to kill itself.
Add new states to ZMap so we can better control interaction with user and
with threads.
Each Zmap can now run multiple threads to contact multiple servers.
Make cleanup code more robust by using state of Zmap and state of threads.