ENH: also test for correct Proj dir settings

Tests/OutOfSource/OutOfSourceSubdir/CMakeLists.txt

@@ -1 +1,4 @@
-ADD_EXECUTABLE (simple simple.cxx)
+IF ("${PROJECT_SOURCE_DIR}" STREQUAL "${ANOTHER_PROJ_SOURCE_DIR}")
+  ADD_EXECUTABLE (simple simple.cxx)
+ENDIF ("${PROJECT_SOURCE_DIR}" STREQUAL "${ANOTHER_PROJ_SOURCE_DIR}")
+