Trace log with a subset of struct conn_state

In struct conn_state, collect together the fields for the remote
address and put them in a substructure.  Pass this substructure to
trace logging macros instead of the entire conn_state structure, so
that trace.c doesn't have to know about the whole structure.
Get rid of cm.c and cm.h

Since net-server.c now uses libverto, only sendto_kdc.c consumes cm.c.
Move stuff out of cm.c and cm.h into sendto_kdc.c and get rid of them.
Change the sendto_kdc callback (used by chpw.c) to receive the socket
descriptor instead of the entire conn_state structure, and move the
declarations into os-proto.h.  struct remote_address also needs to be
in os-proto.h so that trace.c and t_trace.c can use it.  k5_curtime
isn't needed since k5-platform.h now guarantees the presence of
gettimeofday().
Use millisecond timeouts in sendto_kdc.c

Replace the end_time field of struct select_state with an endtime
argument to cm_select_or_poll, expressed in milliseconds since the
epoch.  Add a helper function to get the current time in that format.
Use a millisecond interval argument to service_fds for consistency.

[ghudson@mit.edu: fix overflow issue in get_curtime_ms; service_fds
interval argument change; log message]
Dynamically expand timeout when TCP connects

Wait ten seconds for a TCP connection to succeed or fail before moving
on.  During this wait time, other TCP connections will be serviced if
we already initiated them, but no new TCP connections will be created
and no UDP packets will be retransmitted.

[ghudson@mit.edu: minor adjustments; commit message]

ticket: 7604 (new)