emacs24Macport: new expression

This is "Mac port" addition to GNU Emacs 24. This provides a native GUI
support for Mac OS X 10.4 - 10.9. Note that Emacs 23 and later already
contain the official GUI support via the NS (Cocoa) port for Mac OS X
10.4 and later. So if it is good enough for you, then you don't need to
try this.