import .pro file breaks .ui custom build steps for Incredibuild + Qt 4.6.x

In Qt 4.6.x qmake adds the famous "Rem Incredibuild_foo" comments to the command line of uic. When importing a .pro file the line breaks are gone in the command lines property. That means the custom build step doesn't do anything.

In Qt 4.7.x these comments are missing. But that's another story.