save the mapping base to be able to unmap it (rather than the allocation base) later
save the mapping base to be able to unmap it (rather than the allocation base) later

git-svn-id: d6c3a5d9722f196aef34e75ccf9de8eace0d3e4f@61 1596915d-9e13-0410-ab7f-96e59408e0f0

rboulton/plibc,rboulton/plibc,Karlson2k/PlibC,Karlson2k/PlibC