Avoid msbuild idiosyncrasy that builds multiple configs (#11594)

If a .sln file refers to a project file with a leading ".\", as in
".\foo.vcxproj" instead of just "foo.vcxproj" or a full path then
msbuild behaves strangely.  Whenever target foo is built as a dependency
of another target, msbuild brings multiple configurations up to date
instead of just the requested configuration!

Refer to all project files by full path to avoid this behavior.

Source/cmGlobalVisualStudio7Generator.cxx

@@ -297,8 +297,6 @@ void cmGlobalVisualStudio7Generator::WriteTargetsToSolution(
         {
         cmMakefile* tmf = target->GetMakefile();
         std::string dir = tmf->GetStartOutputDirectory();
-        dir = root->Convert(dir.c_str(),
-                            cmLocalGenerator::START_OUTPUT);
         this->WriteProject(fout, vcprojName, dir.c_str(),
                            *target);
         written = true;