Replace <sys/param.h> with <limits.h> and other less dirty headers where

Replace <sys/param.h> with <limits.h> and other less dirty headers where
possible.  Annotate <sys/param.h> lines with their current reasons.  Switch
to PATH_MAX, NGROUPS_MAX, HOST_NAME_MAX+1, LOGIN_NAME_MAX, etc.  Change
MIN() and MAX() to local definitions of MINIMUM() and MAXIMUM() where
sensible to avoid pulling in the pollution.  These are the files confirmed
through binary verification.
ok guenther, millert, doug (helped with the verification protocol)