Make the OSX 10.6+ release x86_64 only.

We have no need for the 10.6+ bundle to be 32 and 64bit. For older 32bit
machines they should be using the 10.4+ 32bit release.
Merge topic 'build_cmake_dmg_non_universal' into next

3da328d3 Make the OSX 10.6+ release x86_64 only.