invalid type in Number_T::is_zero()

[rwst]

http://trac.sagemath.org/ticket/13326

sage: if log(2)*Infinity == Infinity: print "Hello"
type = 45233600
** Hit STUB**: invalid type: is_zero() type not handled

#6  0x00007fffcc873a79 in GiNaC::Number_T::is_zero (this=0x2b54dd0) at numeric.cpp:935
#7  0x00007fffcc879630 in GiNaC::numeric::is_zero (this=0x2b54db0) at numeric.cpp:1964
#8  0x00007fffcc88e113 in GiNaC::relational::operator void (GiNaC::relational::safe_bool_helper::*)() (this=0x2b23630) at relational.cpp:392
#9  0x00007fffcc398acc in relational_to_bool (e=...)

#8  0x00007fffcc88e113 in GiNaC::relational::operator void (GiNaC::relational::safe_bool_helper::*)() (this=0x2b23630) at relational.cpp:392
392                             return make_safe_bool(ex_to<numeric>(df).is_zero());
(gdb) l
387                     const infinity & lh_inf = ex_to<infinity>(lh);
388                     const infinity & rh_inf = ex_to<infinity>(rh);
389                     const ex df = lh_inf.get_direction() - rh_inf.get_direction();
390                     switch (o) {
391                     case equal:
392                             return make_safe_bool(ex_to<numeric>(df).is_zero());

(gdb) p df.dbgprint()
log(2)/abs(log(2)) - 1
$3 = void
(gdb) p lh_inf.dbgprint()
(log(2)/abs(log(2)))*Infinity
$2 = void

A followup ticket (#36) would be to check positivity of a symbolic factor of infinity in get_direction() in order to get one of -1,0,1 (which as well could be typed and throw an exception if unknown).

Until that ticket is resolved any non-numeric in df should return undecided from relational::safe_bool().