Merge branch 'ExternalProject-checkout-clarify' into release

Modules/ExternalProject.cmake

@@ -601,7 +601,7 @@ if(error_code)
 endif()
 
 execute_process(
-  COMMAND \"${git_EXECUTABLE}\" \${git_options} checkout ${git_tag}
+  COMMAND \"${git_EXECUTABLE}\" \${git_options} checkout ${git_tag} --
   WORKING_DIRECTORY \"${work_dir}/${src_name}\"
   RESULT_VARIABLE error_code
   )