cmTarget: Make the source files depend on the config.

Disallow the use of config-specific source files with
the Visual Studio and Xcode generators. They don't have
any way to represent the condition currently.

Use the same common-config API in cmQtAutoGenerators. While
it accepts config-specific files, it doesn't have to support
multiple configurations yet.

Loop over the configs in cmTargetTraceDependencies
and cmGlobalGenerator::WriteSummary and consume all source
files.

Loop over the configs in cmComputeTargetDepends and compute the
object library dependencies for each config.

Source/cmExtraCodeBlocksGenerator.cxx

@@ -399,7 +399,8 @@ void cmExtraCodeBlocksGenerator
         case cmTarget::UTILITY: // can have sources since 2.6.3
           {
           std::vector<cmSourceFile*> sources;
-          ti->second.GetSourceFiles(sources);
+          ti->second.GetSourceFiles(sources,
+                            makefile->GetSafeDefinition("CMAKE_BUILD_TYPE"));
           for (std::vector<cmSourceFile*>::const_iterator si=sources.begin();
                si!=sources.end(); si++)
             {