Better/more strtol variants

[Roland McGrath]

In general this sort of slight interface improvement is not sufficient
justification to complicate the API with something that duplicates the
functionality of a standards-specified interface.  Most applications will
want to use the standard interface for portability anyway (even just to
this year's glibc-based systems, since a new API wouldn't find its way into
wide deployment for at least a year, probably longer).