Fix definition of CONTROLC0

DEL character is not thecnically talking a C0 control character,
although it has some common properties with them, so it is useful
for us consider it as C0. Before this patch DEL (\177), was not
ignored as it ought to be.

st.c

@@ -70,7 +70,7 @@ char *argv0;
 #define LEN(a)     (sizeof(a) / sizeof(a)[0])
 #define DEFAULT(a, b)     (a) = (a) ? (a) : (b)
 #define BETWEEN(x, a, b)  ((a) <= (x) && (x) <= (b))
-#define ISCONTROLC0(c) (BETWEEN(c, 0, 0x1f))
+#define ISCONTROLC0(c) (BETWEEN(c, 0, 0x1f) || (c) == '\177')
 #define ISCONTROLC1(c) (BETWEEN(c, 0x80, 0x9f))
 #define ISCONTROL(c) (ISCONTROLC0(c) || ISCONTROLC1(c))
 #define LIMIT(x, a, b)    (x) = (x) < (a) ? (a) : (x) > (b) ? (b) : (x)