client:

- Appended -mmacosx-version-min=10.4 to CXX_FLAGS for MacOSX gcc
- Fixed client_package_macosx target in Makefile to always clean the build dirs first.


git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2567 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534