run-tests: replace inline python handling with more native scheme
Normally changes in tests are reported like this in diffs:
$ cat foo
- a
+ b
Using -i mode lets us update tests when the new results are correct
and/or populate tests with their output.
But with the standard doctest framework, inline Python sections in
tests changes instead result in a big failure report that's unhelpful.
So here, we replace the doctest calls with a simple compile/eval loop.
[ original upstream message ]