ports/184224: science/gromacs: Update to version 4.6.4

[wg at FreeBSD.org]

Synopsis: science/gromacs: Update to version 4.6.4

Responsible-Changed-From-To: freebsd-ports-bugs->wg
Responsible-Changed-By: wg
Responsible-Changed-When: Tue Nov 26 17:45:49 UTC 2013
Responsible-Changed-Why: 
I'll take it.

http://www.freebsd.org/cgi/query-pr.cgi?pr=184224