BUG: Need to check "usable" before doing things with the config structure that presume it's been initialized correctly.
FEATURE: Branches are tags too! (Use tag location code to figure out where branches come from)
DESIGNBUG: New revisions with previous timestamps are treated differently by "cache -u" (in which case they're correctly placed after the current revisions) than by "cache -b" (in which case they're placed where the timestamp indicates rather than where they belong).
FEATURE: "cscvs merge". Attempt a dry-run of all diffs for changesets in the given range, and apply each diff if the dry-run succeeds; let the user specify either fail-on-first-conflict or commit-all-nonconflicting behaviour. Re binary files, let the user specify "branch-always-overrides", "ignore-binary-files", or "break-on-binary-files".
