[boost] [boost-build] feature request for qt4.jam

A suggestion for qt4.jam file is to create/separate out the inc/bin/lib prefix variables rather than hardcode .prefix/include/QtXXXXX in the sections. My distro puts things in /usr/include/qt4/QtXXXXX so I end up having to modify this file. I'm not sure what the correct solution is for this, but at least if there were separate prefix variables, I could just change a couple of lines rather than multiple places in the script. Overall, this support makes building QT apps a snap. Thanks for providing it. Brian