string->number wrong parsing of numbers with sign in the middle

[marcomaggi]

The following forms should return false:

(string->number "1-1") => 1-i
(string->number "1.2-3.4") => 1.2-3.4i

but notice that:

(string->number "1/2-3/4") => #f

The problem shows up in source files reading, too, because the code of STRING->NUMBER is used also by the reader.

[marcomaggi]

Should be fixed in the ikarus and devel branches.