Add a dmg_package_prep target as an alias to app_bundle. Rename the
osx-dmg target to dmg_package. This matches the Windows packaging
target names.
In osx-app.sh, make sure we rpathify the bundle plugin directory.
Change-Id: If41195c9d405ad6bff865625500a8227b77e8092
Reviewed-on: https://code.wireshark.org/review/10734
Reviewed-by: Gerald Combs <gerald@wireshark.org>