Draw the insides of ignored loops with nested loop boxes.
Add an ignore-loop-and-all-children option, document a few more syscalls, and have another go at keeping BAA safe but moderately informed.

Specifically I replace the header-phis-may-alias rule with one that lowers header phis into their equivalent at parent scope, thus ensuring we consider all possibilities for such a PHI. We should already be considering the root in that way if we approached the loop from outside, since BAA's getValOperand never rises.
Add a slightly stronger version of BAA's non-escaping-object test: objects which are only ever used directly (i.e. via GEPs and casts only) cannot alias unresolved PHI or select instructions.

Also experimentally enable automatically pursuing functions in invariant context