title: VS2013 debugger can not find Qt sources
body: <p>I am using Visual Studio 2013 for building Qt5.3.1 projects. I use the express version so I don't use the VS plugin. My .vcxproj files a generated from .pro files using build scripts and qmake.</p>
  
  <p>I installed Qt 5.3.1 with the default offline installation package that can be downloaded from the project pages. During installation I enabled sources to be installed (which are not installed by default).</p>
  
  <p>When debugging my projects I sometimes try to step into Qt library code. This unfortunately does not work anymore (I know it once worked for some older Qt version but I can't name it). 
  The .pdb files are found (I checked this in VS modules view) but the source files are not found. Whenever I step into Qt library code the debugger asks me to search the needed source file manually using a file dialog. If I select the proper .cpp file somewhere in the Qt folder the debugger works fine and I can step through the code. Unfortunately I need to repeat this for every Qt library source file and it is pretty annoying.</p>
  
  <p>Is there a way to tell VS how to find the sources files in the Qt folder by itself?</p>