MFC r207485: pathchk(1): Fix the example so it allows arbitrary pathnames.

MFC r207485: pathchk(1): Fix the example so it allows arbitrary pathnames.

Spaces and various other characters in pathnames are not passed through
literally by xargs in its default mode. Instead, use find . -exec ... {} +

Although the -- argument is not strictly required here, add it anyway to
avoid surprises when modifying the code to find -f -somedir ...

git-svn-id: svn://svn.freebsd.org/base/stable/8@207827 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f