lint logically inconsistent checks

e.g. x == 10 && x == 0, or checks that can be simplified, e.g. x > 10 && x > 12 (which can be simplified to x > 12). This requires a RangeSet implementation (there is range_map, but it works only for integers and doesn't allow adding a Range, strangely) over constant values, as well as a bit of cleverness to find out if checks are inconsistent or needless.

The idea is to decompose the expression on || / && subexpressions, and check their operands. For example:

• x > 3 && x < 3 is a falsity
• x > 3 && x > 5 can be reduced to the latter subexpression because it is fully contained in the former
• x < 3 || x >= 3 is tautological