Fixed a regression causing libxdispatch not to be linked against libdispatch whenever a pre-installed libdispatch version is detected

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@576 9e4c620c-c391-4b63-a7fb-4924991ea895
Added the option to selectively disable blocks, lambda or std::function support

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@580 9e4c620c-c391-4b63-a7fb-4924991ea895
An experimental new exception handler

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@581 9e4c620c-c391-4b63-a7fb-4924991ea895