1. using SIDs (service IDs) to communicated with external processes

   This was a very bad idea: The external program could exploit us by
   specifying an arbitary big SID (as the SID is simply the index
   of our service array).

2. using function pointers to handle messages
   
   Seems like it works fine. We have handlers for each
   message (do_*), which are called by client and server.
   The function pointer is simply to read or write, dependending
   if it is the client or the server. This way we don't need
   to rewrite communications parts.

3. Using different storage
   
   First all services were saved in a service array of the size
   MAX_SVC. This has been replaced by a double-linked list.
   Have a look at serv/list.c.

4. Using sockets for IPC (between cinit forks)
   
   Works very fine, though we have to mount a temporarily fs before.