bufio: make scanning bounded and incremental

test/wcc/data/r778_scanner_byte_bytes/case.ww

@@ -3,6 +3,7 @@
 package main;
 import os;
 import bufio;
+import errors;
 import memio;
 import io;
 export fn main() i32 = {
@@ -18,20 +19,20 @@ export fn main() i32 = {
     case let b: u8 => { fb = b; };
     case io.eof => { return 81; };
     case let e: io.error => { return 82; };
-    case bufio.overflow => { return 92; };
+    case errors.overflow => { return 92; };
     };
     if (fb != 65u8) { return 83; };
     match (bufio.scanbytes(&sc, 44u8)) {
     case let bs: []u8 => { if (bs.len != 1 || bs[0] != 66u8) { return 84; }; };
     case io.eof => { return 85; };
     case let e: io.error => { return 86; };
-    case bufio.overflow => { return 87; };
+    case errors.overflow => { return 87; };
     };
     match (bufio.scanbytes(&sc, 44u8)) {
     case let bs: []u8 => { if (bs.len != 2 || bs[0] != 67u8 || bs[1] != 68u8) { return 88; }; };
     case io.eof => { return 89; };
     case let e: io.error => { return 90; };
-    case bufio.overflow => { return 91; };
+    case errors.overflow => { return 91; };
     };
     return 53;
 };