callbacks wip: nested callbacks for body queries
tests: testing gc within callback

just in case the GC would confuse things
cleanup minor: fixes indentation
test cleanup: make raytrace/point-query sample into test
callback wip: allow nesting space-point-query calls
callback wip: allow nested callbacks for space-for-each-bb-query

now we've only got segment-query left!
callback minor: adds macro assertions

helps me along as I confuse myself
doc: minor cleanup in comments
bugfix, critical: fixes centroid-for-poly, adds test
cleanup: uses vmult instead of v* for consistency

trying to stick to the Chipmunk naming conventions. v* may not be part
of our "stable" api (the glm egg, for example, has a v* function). safer
to stick with Chipmunk names.
callback: nested callbacks for space-segment-query w/tests

- we're not using any globals anymore, yey!
- we can delete start-safe-callbacks and friends
- we must still handle exceptions in callbacks (space doesn't get
- unlocked otherwise)
tests fix: exit with correct exit-code
samples: fixes glut-sample

but I don't know if glut-sandbox still works...
callback cleanup: removes dead syntax
nodes fixup: reindexes shape after added

this makes tests run. without this, point-query and segment-query tests
fail. we always reindex a space after adding nodes so that such queries
work without space-step first.