Make `compute-addresses` less clever. Stop striding from the middle of
one row to the next. This way we'll also obviate the need for indexing
backwards from a pointer in the next commit.
Kinda hacky, but might scale enough for machine code.
This was really hard to debug. Single tests passed, but when I ran all
tests I got breakage because tests long before (from the 056trace layer)
were not cleaning up properly.
My instinct was to call clear-stream on Trace-stream, which was wrong
(the trace didn't have the wrong contents, it was literally a bad
object). It was also wrong in a counter-productive way: calling
clear-stream on a real Trace stream (which is the size of a page of
memory) takes a long time in emulated mode.
'get-or-insert-stream' is now the more generic 'get-or-insert' that can
handle tables of any value type. But callers have to be careful to cast
values to the right type.
Start of the final phase needed to implement SubX in SubX:
$ cat files.subx ... |dquotes |assort |pack |survey |hex > a.elf
survey.subx is responsible for assigning addresses to labels and segments.
