travis: Use unified diffs for failed tests.
binary: machine_uint_t vs uint dichotomy starts doing real damage.
py: Add portable framework to query/check C stack usage.

Such mechanism is important to get stable Python functioning, because Python
function calling is handled with C stack. The idea is to sprinkle
STACK_CHECK() calls in places where there can be C recursion.

TODO: Add more STACK_CHECK()'s.
stmhal: Use stackctrl framework.