Be smarter about element types
Merge the two changes mentioned in #25 to improve element-type handling.
I've tested this merge as well as this merge combined with !22 (merged) (for #24 (closed)) with LW 7.1.3 (mac) CCL 1.12.1 (mac), SBCL 2.1.9 (Linux), and I think they're both fine. I think someone else should probably check them though.
Closes #25