MFC r320267, r320270-r320271, r320478

r320267:
Do not use sprintf(3) when not needed, while here,
prefer snprintf(3) over sprintf(3)

r320270:
Directly print the extra status instead of filling a buffer
then printing it.

This prepares the code to make it libxo friendly

Reviewed by: manu, Nikita Kozlov (nikita elyzion.net)
Sponsored by: Gandi.net

r320271:
sesutil no longer depends on libsbuf

Sponsored by: Gandi.net

r320478:
Add libxo(3) support to sesutil(8)

This is useful to simplify parsing "sesutil map"

Submitted by: nikita.kozlov@blade-group.com
Relnotes: yes
Reviewed by: Allanjude, bapt
Differential revision: https://reviews.freebsd.org/D11372
Sponsored by: blade