use framework absolute path, do not copy headers into final product

git-svn-id: svn+ssh://svn.savannah.nongnu.org/gap/trunk@2795 d25b4930-3292-e311-b074-0010c6de5da8
improve mac version detection

git-svn-id: svn+ssh://svn.savannah.nongnu.org/gap/trunk@2796 d25b4930-3292-e311-b074-0010c6de5da8