Implement xstrncat() and fix xstrndup().
Work with buildroot's extensively patched uClibc, and for nommu support move xfork() to portability.h and #ifdef based on __uClinux__ (which seems to be the nommu compiler define).
Fix some sed bugs and improve error reporting.

A newline after 'b' commands in -e command line patterns was being discarded
as whitespace, a single element regex match on a {} was leaving stale state
for the next line, and giant -e blobs of instructions were saying things
like problem at character 432 (note: nulls inserted for regex processing
aren't always cleaned up, screws up error reporting).
Make unescape_delimited_string() copy the string so error reporting isn't so messed up.
here's a patch that should let us replace toolbox's chcon.
(it also adds a feature, -R, because toybox makes that so easy.)

you'll probably want fancier configuration here because although the
--as-needed works okay, a typical Ubuntu box will have the .so but not
the .h files. i did consider adding a toys/selinux/ directory, but
given that existing tools like ls and id will want -Z SELinux options,
i wasn't sure whether you'd think it was worth segregating the
SELinux-only toys.

note that this won't help the tizen smack users (and patch for smack
won't help SELinux users). so you might want to think about where
you'd like us to be aiming: #if USE_SELINUX/USE_SMACK in all the
relevant places, or a toys/selinux and a toys/smack (though we'd still
need #if in at least ls and id), or a lib/security.c that concentrates
all the differences into one file?