Increase revision from 'b' to 'c'.

For now, even if you managed to build v3.15c, you should not use it.

src/sbbs3/sbbsdefs.h

@@ -51,7 +51,7 @@
 /*************/
 
 #define VERSION 	"3.15"  /* Version: Major.minor  */
-#define REVISION	'b'     /* Revision: lowercase letter */
+#define REVISION	'c'     /* Revision: lowercase letter */
 #define VERSION_NUM	(31500	 + (tolower(REVISION)-'a'))
 #define VERSION_HEX	(0x31500 + (tolower(REVISION)-'a'))