server/: Split peer and admin initialization into smaller pieces.

server/: Split peer and admin initialization into smaller pieces.

Split admin initialization into:

  * setting up internal data structures, which is `a_init' as before;

  * establishing the daemonic signal handlers, which is now `a_signals';

  * creating the admin socket and listening for incoming connections,
    which is now `a_listen'; and

  * switching alert reporting over to admin clients rather than stderr,
    which is now `a_switcherr'.

Given that `a_listen' now need not actually be called, only unlink the
socket object if we actually created it.

Split peer initialization into:

  * setting up the data structures, which is `p_init' as before; and

  * creating the UDP sockets for communicating with other peers, which
    is now `p_bind'.

This will make sense in context.

squash! server/: Split peer and admin initialization into smaller pieces.

server/admin.c: Split out signal-handler establishment.