Resolve warnings on Windows

Appease the compiler by resolving some of the reported warnings,
including:

- Control paths that don't return.

- Potentially uninitialized variables.

- Unused local variables.

- Unreachable code.

- Type safety.

- Synchronize declarations with definitions for functions.

lib/roken/unvis.c

@@ -126,7 +126,7 @@ rk_unvis(char *cp, int c, int *astate, int flag)
 			*astate = S_OCTAL2;
 			return (0);
 		case 'M':
-			*cp = (char)0200;
+			*cp = (u_char)0200;
 			*astate = S_META;
 			return (0);
 		case '^':