Revert "added unsigned to char s_foo"

breaks my build:

types.h: In function `char * KEYMAX()':
types.h:955: return to `char *' from `unsigned char *' changes signedness
In file included from gb-include.h:16,
                 from Tfndb.cpp:1:
types.h: In function `char * KEYMAX()':
types.h:955: return to `char *' from `unsigned char *' changes signedness
make: *** [Mime.o] Error 1
make: *** Waiting for unfinished jobs....
make: *** [Tfndb.o] Error 1
In file included from gb-include.h:16,
                 from UdpSlot.cpp:1:
types.h: In function `char * KEYMAX()':
types.h:955: return to `char *' from `unsigned char *' changes signedness
In file included from gb-include.h:16,
                 from Msg13.cpp:1:
types.h: In function `char * KEYMAX()':
types.h:955: return to `char *' from `unsigned char *' changes signedness
make: *** [UdpSlot.o] Error 1
make: *** [Msg13.o] Error 1

This reverts commit 50af82deb382df31d01e1aa7523105f7a73bb4fd.