build: Install some more files to their eventual locations.

Install the base peers.in file as ${configdir}/peers.d/10base as a
convenience to users.  It's correct to clobber the user's old file,
since there's a fierce warning at the top of the file.  (Make the
warning more fierce.)

Install the startup script configuration file (but not the script
itself), only if there isn't one already.  This prevents us from
overwriting a user's customized configuration.

To prevent distcheck from failing, change the default of `initconfig' to
be ${sysconfdir}/tripe.conf; this is probably the right thing anyway.