[CMake] Qt4 support

[John Biddiscombe]

> If changed, they'd probably be QT4_WRAP_CPP QT4_WRAP_UI.  I don't 
> think compatibility between Qt3 cmake and Qt4 cmake is a bit deal 
> because I think most projects will be exclusivly Qt3 OR Qt4, because 
> of major Qt API changes.

I'm finding that I have a main root dir containing cmakelists, within 
that, there are many subdirs. Most gui based apps in subdirs are using 
Qt3, but I've started redoing one in qt4, I'm therefore finding that 
currently, I have problems building using both. life would be easier if 
coexistence were possible.

[Also, I'm not saure that QT_WRAP... should be part of cmake anyway. As 
macros, they're fine, but it's strange that core cmake calls are so 
specific., just my $0.02]

The macro approach is working very well for me.

JB