bksys/generic.py cleanup

[Ralf Habacker]

Hi all,

when I create a Makefile for qt's examples (for example 
examples\network\blockingfortuneclient) and compare the resulting 
preprocesser definitions I see three definitions, which are not covered 
by recent detect_qt4.py

-DQT_DLL -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN

I suggest to set this in env['CXXFLAGS_QT']. Are there any problems to 
expect ?

Ralf