pw should sanitize the argument of -w.

pw should sanitize the argument of -w.

Otherwise, it will silently disable the login for the selected account if
the argument is unrecognizable.

usr.sbin/pw/pw.h
usr.sbin/pw/pw_conf.c
usr.sbin/pw/pw_user.c
	Use separate rules to validate boolean parameters and passwd
	parameters.  Error out if a password parameter cannot be parsed.

usr.sbin/pw/tests/Makefile
usr.sbin/pw/tests/crypt.c
usr.sbin/pw/tests/pw_useradd.sh
usr.sbin/pw/tests/pw_usermod.sh
	Add tests for the validation.  Also, enhance existing
	password-related tests to actually validate that the correct hash is
	written to master.passwd.

Reviewed by:	bapt
MFC after:	4 weeks
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D6840