OSX: Make the "Get Info" dialog show the build date and git version

and at the same time give a more sane value for creation and
modification times. The later seem to be based on a collective sifting
of the whole application tree, so I touch everything just before
zipping it up.
Merge pull request #660 from monkeyiq/2013aug/osxmetadata

OSX: Make the "Get Info" dialog show the build date and git version