qsort()-style function that returns negative if lhs is less than
rhs, positive if lhs is greater than rhs, and 0 if they're equal.
Ordering is in character offset order, i.e. the first character in the buffer
is less than the second character in the buffer.gtkTextIterCompare(object, rhs)objectrhsGtkTextIterlhs is less than rhs, 1 if lhs is greater, 0 if they are equal