docs/157078: [patch] su.1: clarify use of -c as shell argument

[gjb at FreeBSD.org]

Synopsis: [patch] su.1: clarify use of -c as shell argument

Responsible-Changed-From-To: freebsd-doc->gjb
Responsible-Changed-By: gjb
Responsible-Changed-When: Mon Jun 6 14:42:58 UTC 2011
Responsible-Changed-Why: 
I'll take this.


http://www.freebsd.org/cgi/query-pr.cgi?pr=157078