Changelog for 3.0-791

fix Snow Leopard compatibility

Checking for clang in Xcode bundle seems pointless, command line tools should be installed.
Setting the path explicity to avoid fink/macports/homebrew prevents use of locally installed packages like clang and wxwidgets.
Realistically using opencl means the minimum OSX version targetable is 10.6.
Correct TARGET_SYSROOT check, add required -mmacosx-version-min to linker flags.
also using wxwidgets gl component.