Moved -g -ggdb to global gcc-compatible build flags.

Without these, profiling isn't meaningful. We're going to have to strip
binaries as a post-process anyway, so even if this modifies the contents,
it will come out during strip.
math: Removed superfluous init in box.

There were already comments about box not initing. Now it really doesnt, and
avoids writing values that are overwritten during set, if set is called during
ctor.
quadtree demo: Cosmetic changes to animation coefs.