Add formula for clens 0.7.0

clens is a convenience library to aid in porting code from OpenBSD
to different operating systems. The patch that's refenced in this
formula has already been applied upstream, but no new release has
been made yet.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
mg 20130922

This brings in two years of fixes and features for mg.

Closes #23862.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
mg 20131118