(15708) use pkgbuild to create mac packages

Now that PackageMaker is deprecated, update apple task to use pkgbuild instead.

Also, rename {pre,post}flight scripts to {pre,post}install so they'll work with pkgbuild packages.
Remove PackaeMaker stanza
Make sure preinstall script is executable.
Merge pull request #171 from ccaviness/fix/master/use_pkgbuild

(15708) use pkgbuild to create mac packages