MFC: r285133,r285136,r285137,r285156,r285157,r285158,r285256,r285318,r285395,

MFC: r285133,r285136,r285137,r285156,r285157,r285158,r285256,r285318,r285395,
r285396,r285398,r285401,r285403,r285405,r285406,r285408,r285409,r285411,
r285412,r285413,r285415,r285418,r285430,r285433,r285434,r285442,r285948,
r285984,r285985,r285989,r285996,r285997,r286045,r286047,r286066,r286150,
r286151,r286152,r286154,r286155,r286156,r286157,r286173,r286196,r286197,
r286198,r286199,r286200,r286201,r286202,r286203,r286204,r286210,r286211,
r286217,r286218,r286258,r286259,r286341,r286775,r286982,r286986,r286991,
r286993

Validate most pw inputs.
Rewrite the way parsing sub arguments is made to simplify code and improve
maintenability
Add -y (NIS) to userdel/usermod
pw userdel -r <rootdir> now deletes directories in the rootdir
Only parse pw.conf when needed
Reject usermod and userdel if the user concerned is not on the user database
supposed to be manipulated

git-svn-id: svn://svn.freebsd.org/base/stable/10@287084 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f