Update to r42973:

This patch finishes up the NIS section of this chapter. It does the following:

• replaces NISv1 Compatibility section with a note that FreeBSD uses v2
• renames Important Things to Remember to Adding New Users and places it as a subsection of Configuring the NIS Master Server
• removes the reference to auth.log which is now obsolete
• general tightening and clarification

Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D5856