Add CJK codecs support as discussed on python-dev. (SF #873597)

Several style fixes are suggested by Martin v. Loewis and
Marc-Andre Lemburg. Thanks!
diff --git a/Modules/cjkcodecs/_cp949.c b/Modules/cjkcodecs/_cp949.c
new file mode 100644
index 0000000..f2fa38c
--- /dev/null
+++ b/Modules/cjkcodecs/_cp949.c
@@ -0,0 +1,73 @@
+/*
+ * _cp949.c: the CP949 codec
+ *
+ * Written by Hye-Shik Chang <perky@FreeBSD.org>
+ * $CJKCodecs: _cp949.c,v 1.2 2003/12/31 05:46:55 perky Exp $
+ */
+
+#include "codeccommon.h"
+
+ENCMAP(cp949)
+DECMAP(ksx1001)
+DECMAP(cp949ext)
+
+ENCODER(cp949)
+{
+    while (inleft > 0) {
+        Py_UNICODE  c = IN1;
+        DBCHAR      code;
+
+        if (c < 0x80) {
+            WRITE1(c)
+            NEXT(1, 1)
+            continue;
+        }
+        UCS4INVALID(c)
+
+        RESERVE_OUTBUF(2)
+        TRYMAP_ENC(cp949, code, c);
+        else return 1;
+
+        OUT1((code >> 8) | 0x80)
+        if (code & 0x8000)
+            OUT2(code & 0xFF) /* MSB set: CP949 */
+        else
+            OUT2((code & 0xFF) | 0x80) /* MSB unset: ks x 1001 */
+        NEXT(1, 2)
+    }
+
+    return 0;
+}
+
+DECODER(cp949)
+{
+    while (inleft > 0) {
+        unsigned char    c = IN1;
+
+        RESERVE_OUTBUF(1)
+
+        if (c < 0x80) {
+            OUT1(c)
+            NEXT(1, 1)
+            continue;
+        }
+
+        RESERVE_INBUF(2)
+        TRYMAP_DEC(ksx1001, **outbuf, c ^ 0x80, IN2 ^ 0x80);
+        else TRYMAP_DEC(cp949ext, **outbuf, c, IN2);
+        else return 2;
+
+        NEXT(2, 1)
+    }
+
+    return 0;
+}
+
+#include "codecentry.h"
+BEGIN_CODEC_REGISTRY(cp949)
+    MAPOPEN(ko_KR)
+        IMPORTMAP_DEC(ksx1001)
+        IMPORTMAP_DEC(cp949ext)
+        IMPORTMAP_ENC(cp949)
+    MAPCLOSE()
+END_CODEC_REGISTRY(cp949)