Add headers to resolve implicit declaration warnings.

clients/fax500/rp500.c

@@ -14,6 +14,7 @@
 
 #include <stdlib.h>
 
+#include <ac/ctype.h>
 #include <ac/signal.h>
 #include <ac/socket.h>
 #include <ac/string.h>

clients/mail500/main.c

@@ -22,6 +22,8 @@
 #include <ac/wait.h>
 #include <ac/unistd.h>
 
+#include <sys/stat.h>
+
 #ifdef HAVE_SYS_PARAM_H
 #include <sys/param.h>
 #endif

clients/ud/util.c

@@ -14,6 +14,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <fcntl.h>
 
 #include <ac/ctype.h>
 #include <ac/errno.h>