Comparison operators with incompatible types should return undefined instead of raising an exception

[josephbirkner]

Currently, using comparison operators with unsupported pairs of types raises an exception. E.g. 50 > "a" raises a simfil InvalidOperandsException. It would be more practical, if this operation would simply assume the value undefined. This way, a structure like {a: {x: 50}, x: "a"} (containing ambiguous value types for the same field name) could more easily be matched with a query like **.x > 0.