and exit points. 2. Simplify bigcomp comparison loop. 3. Don't set
ERANGE on _Py_dg_strtod underflow (it was set inconsistently anyway).
4. Remove unused dsign field from BCinfo struct.
Also remove some now unused variables, and add comments clarifying the
possible outputs of the parsing section of _Py_dg_strtod. Thanks
Eric Smith for reviewing.