VS: Set WindowsPhone and WindowsStore min VS version required

Generate the MinimumVisualStudioVersion element in the .vcxproj file
based on the version of WindowsPhone or WindowsStore to be targeted.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -2120,5 +2120,17 @@ void cmVisualStudio10TargetGenerator::WriteApplicationTypeSettings()
     this->WriteString("<ApplicationTypeRevision>", 2);
     (*this->BuildFileStream) << cmVS10EscapeXML(v)
                              << "</ApplicationTypeRevision>\n";
+    if(v == "8.1")
+      {
+      // Visual Studio 12.0 is necessary for building 8.1 apps
+      this->WriteString("<MinimumVisualStudioVersion>12.0"
+                        "</MinimumVisualStudioVersion>\n", 2);
+      }
+    else if (v == "8.0")
+      {
+      // Visual Studio 11.0 is necessary for building 8.0 apps
+      this->WriteString("<MinimumVisualStudioVersion>11.0"
+                        "</MinimumVisualStudioVersion>\n", 2);
+      }
     }
 }