Adding header files to a project with many configurations is VERY slow in VS 2010

When adding a header file to a Visual Studio project that has many project configurations, Visual Studio 2010 will become unresponsive for a long period of time, though eventually will succeed at adding the header file and all necessary moc files.

With about 6 configurations it takes around 2 minutes to become responsive again, with 30 configurations it takes about 20 minutes to respond after adding one header file. This time increases if you add multiple header files at the same time.

To reproduce:

• Get a VS 2010 project that has many configurations
• Find a header file that will require moc'ing
• Add the existing header file to the project by right clicking on the Header Files folder in the directory, and saying add existing file.

Not sure what takes it so long, but if it were possible to make the process multi-threaded so that adding multiple files at the same time went faster, that would be a huge improvement over the current state.

This issue becomes a real annoyance when you add a new configuration to a project, and the moc steps are not automatically created for the the existing header files in the project (maybe another bug should be written for this issue). So to have the moc steps created for the new configurations we remove all the header files in the project and re-add them to the project, and this is where the slowness occurs.