Completed 'cleanpackages' stage

These files were not removed:
xcode_3.2.6_llvm-gcc4.2.pkg
Xcode107SDK.tar.gz
XcodePluginGCC42-Xcode4.tar.gz
XcodePluginGCC42.tar.gz
XcodePluginLLVMGCC42.tar.gz

Added mention of SDK 10.7 to ‘usage’.