test_float_overflow(): make shuge (added last week) a little less

test_float_overflow(): make shuge (added last week) a little less
huge.  On older Linux systems, the C library's strtod() apparently
gives up before seeing the end of the string when it sees so many
digits that it thinks the result must be Infinity.  (It is wrong, BTW
-- there could be an "e-10000" hiding behind 10,000 digits.)  The
shorter shuge still tests what it's testing, without relying on
strtod() doing a super job.