support libprefix

the concept of 'libprefix' essentially creates a second version of Qt with a prefix for filenames and different UIDs (beware, there is only one alternative set allowing exactly two versions on a symbian install).

Using the makefile based system this concept is not supported. Its added to the configure script but it doesn't work because the flags passed to the the linker etc are not found due to changing the name. Also qmake is not altered so the UID of Qt which external applications depend on are not changed.