353 - found lots of holes in array support

I've uncovered a few while enhancing 'interpolate', but I'll wait to fix
them all before I commit the enhancements.
354 - stepping back, test-driving 'addr' helper again
355
356 - high time 'sizeof' supported operands
357
358 - start of 'sizeof' support for arrays
359 - 'sizeof' supports 'deref' pointers

Just non-arrays for now.
360 - back up, let's create a new 'deref' helper
361 - *now* 'sizeof' on array pointers
362

Gaining confidence..
363
364
365 - new primitives let us generalize 'addr'
366 - reorg run's helpers

First step to using our new 'deref' and 'absolutize' helpers more
coherently.
367 - start of unit tests for 'm'
368 - replace 'sz' with our new 'sizeof'
369
370 - unit tests for 'setm'
371 - bugfix: don't read destination when writing array

Finally we've gotten to one of the top-level bugs uncovered by
'interpolate'.
372 - size check for arrays