[scponly] optreset variable is not provided by standard glibc

[Jeroen Scheerder]

 :

> My Linux box has glibc version 2.3.6.
> Build of scponly 2.4 fails at linking of helper.o
> because helper.c uses undefined optreset variable
> for control getopt() call.
> 
> How to workaround this?

Change the "extern int optreset" declaration to "int optreset",
probably.