Fix jet mismatches and crashes

[Quodss]

Resolves #700.

[joemfb]

While you're at it, the +swp jet from #577 doesn't check the bloq size. I keep forgetting to fix that.

[Quodss]

This PR will also fix comparison jet mismatches (lth, gth, lte, gte, min, max, mentioned in #699 ) when both inputs are equal cells

[Quodss]

A couple of other mismatches I found: ++dvr crashes the runtime unrecoverably, ++div exits on input [0 0 0] even though it should return 0. Proposal: make the core "type checks" more rigorous in u3w-prefixed jet functions, and return u3_none instead of exiting. I'll commit an example with ++add