string->number should not signal error

[dcurrie]

R7RS says: If string is not a syntactically valid notation for a number, or would result in a number that the implementation cannot represent, then string->number returns #f. An error is never signaled due to the content of string.

> (string->number "-e3")
error: invalid string given: -e3
> (string->number "-e3e4")
error: invalid string given: -e3e4
> (string->number "-")
error: invalid string given: -

BTW, this defect pre-dates the ATOD DTOA changes.

I have a patch coming to fix this defect.