Add "PKGNAME=mosaic-2.6". The DISTNAME of this port is "Mosaic-src-2.6",
which is inappropriate as a package name because:

(1) It contains the string "src"
(2) A simple package is not allowed to have a name that starts with a

capital letter.  Remember, uppercase names are reserved for large
software packages (Wnn, ImageMagick, etc.)!