Add deflateGetDictionary() function.

Per request, but its utility is likely to be very limited. See the
comments in zlib.h.

deflate.c

@@ -440,6 +440,27 @@ int ZEXPORT deflateSetDictionary (strm, dictionary, dictLength)
     return Z_OK;
 }
 
+/* ========================================================================= */
+int ZEXPORT deflateGetDictionary (strm, dictionary, dictLength)
+    z_streamp strm;
+    Bytef *dictionary;
+    uInt  *dictLength;
+{
+    deflate_state *s;
+
+    if (deflateStateCheck(strm))
+        return Z_STREAM_ERROR;
+    s = strm->state;
+    uInt len = s->strstart + s->lookahead;
+    if (len > s->w_size)
+        len = s->w_size;
+    if (dictionary != Z_NULL && len)
+        zmemcpy(dictionary, s->window + s->strstart + s->lookahead - len, len);
+    if (dictLength != Z_NULL)
+        *dictLength = len;
+    return Z_OK;
+}
+
 /* ========================================================================= */
 int ZEXPORT deflateResetKeep (strm)
     z_streamp strm;