Use setuid/seteuid around dangerous operations. Also a few buffer

Use setuid/seteuid around dangerous operations.  Also a few buffer
overflow patches that were "near" to where these operations are taking
place.  The buffer overflows are from OpenBSD.  The setuid/seteuid patches
are from NetBSD by way of OpenBSD (they changed them a little), at least from
my read of the tree.

This is the first of a series of OpenBSD lpr/et al merges.  It (and them)
should be merged back into 2.2 and/or 2.1 (if requested) branches when they
have been shaken out in -current.
Obtained from: OpenBSD