* contrib/lisp/org-export.el (org-export-get-inbuffer-options): Fix
but with incomplete macros returning an error. Also with behaviour
`nil', only insert new value if none was defined before.
(org-export-use-select-tags-p): Fix bug preventing it from properly
detecting select-tags.
(org-export--skip-p): Small refactoring
* testing/contrib/lisp/test-org-export.el: New test file.