Revert "OSX: Only enable @rpath support on OS X 10.6 or greater."

This reverts commit 36c509b9c23725a9e731b4f68a5bfb209bf3cfa1.
OSX: Warn when attempting to change runtime paths on OS X 10.5

Even though 10.5 supports @rpath, the support is not complete
enough for CMake.  For instance, install_name_tool doesn't support
adding and removing rpaths.

Also modifying BundleUtilities test to remove an undesirable cmake
generated runtime path.  The intent was to build with the install
rpath as is done with the other cases in this test.
Merge topic 'rpath-osx-10_6' into next

30c103d2 OSX: Warn when attempting to change runtime paths on OS X 10.5
98cb337e Revert "OSX: Only enable @rpath support on OS X 10.6 or greater."