Changed connection errors to ENOTCONN, updated man pages and unit test.

Added errno set in buxtond_set_group for failure to create a group.
Added changes to man pages reflecting change from EBADMSG to ENOTCONN,
and a note that EBADMSG from buxtond_set_group doesn't necessarily
mean a complete failure. Removed non-existent functions from
check_buxtonsimple.c.