Fix sprintf() type warnings/errors.

src/sbbs3/scfg/scfgchat.c

src/sbbs3/scfg/scfgmsg.c

src/sbbs3/scfg/scfgnet.c

src/sbbs3/scfg/scfgsub.c

src/sbbs3/scfg/scfgsys.c

src/sbbs3/scfg/scfgxfr2.c

src/sbbs3/scfg/scfgxtrn.c