libqxt qmake project files use += instead of *=

[Former user]

This was causing a Windows build problem for us because of excessively long include paths. The solution was to change all += to *= in our project. (http://stackoverflow.com/questions/14641929/what-does-it-mean-in-pro-file-qt)

This meant changing several libqxt files, too. We're using an old version of libqxt so our patches wouldn't work for you, but I hope this information will be of use to you.