Makes the parser favour integer possibilities in ambiguous terms.
DESCRIPTION
Calling prefer_int() causes the global grammar to be altered so that
the standard arithmetic operator symbols (+, *, etc.), as well as
numerals, are given integral types if possible. This effect is
brought about through the application of multiple calls to
temp_overload_on, so that the “arithmetic symbols” need not have
been previously mapping to integral possibilities at all (as would be
the situation after a call to deprecate_int).