Changes from 1.2 to 1.3:

Changes from 1.2 to 1.3:
  - reverted or/c to union, since we can't rely on or/c being present in
    all v300 systems.  Have to rethink this transition.

Changes from 1.1 to 1.2:
  - Fixed packaging error that omitted contract-utils.ss.

Changes from 1.0 to 1.1:
  - Added version spec to doc.txt, source code
  - Replaced union contract operator (now deprecated) with or/c
  - Added license clarification to contract-utils.ss.