Added setuid callback to startup structure.

src/sbbs3/ftpsrvr.c

src/sbbs3/ftpsrvr.h

src/sbbs3/mailsrvr.c

src/sbbs3/mailsrvr.h

src/sbbs3/main.cpp

src/sbbs3/sbbscon.c

src/sbbs3/services.c

src/sbbs3/services.h

src/sbbs3/startup.h