New platform feature mechanism detection

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@637 9e4c620c-c391-4b63-a7fb-4924991ea895
Rewrote xdispatch and qtdispatch to make use of the new platform detection. Helped to reduce a lot of duplicated code. Still needs a lot of testing

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@638 9e4c620c-c391-4b63-a7fb-4924991ea895
Follow-Up to last commit: Some tuning for the new features

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@639 9e4c620c-c391-4b63-a7fb-4924991ea895
Fixed several compilation issues discovered when using gcc-llvm 4.2 on Mac OS X 10.6

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@640 9e4c620c-c391-4b63-a7fb-4924991ea895
Fixed a regression causing some tests not to be enabled despite support

git-svn-id: http://opensource.mlba-team.de/svn/xdispatch/trunk@641 9e4c620c-c391-4b63-a7fb-4924991ea895