ports/182566: Fix mail/dbmail not building with DOCS unset

[wg at FreeBSD.org]

Synopsis: Fix mail/dbmail not building with DOCS unset

Responsible-Changed-From-To: freebsd-ports-bugs->wg
Responsible-Changed-By: wg
Responsible-Changed-When: Wed Oct 2 14:12:50 UTC 2013
Responsible-Changed-Why: 
I'm sorry, I did the last commit and converted to staging, its my fault.
I'll take it.

http://www.freebsd.org/cgi/query-pr.cgi?pr=182566