skip creating intermediate ruby string for symbol keys on 1.9+

Author: brianmario

ext/mysql2/result.c

@@ -114,15 +114,18 @@ static VALUE rb_mysql_result_fetch_field(VALUE self, unsigned int idx, short int
 
     field = mysql_fetch_field_direct(wrapper->result, idx);
     if (symbolize_keys) {
-      VALUE colStr;
       char buf[field->name_length+1];
       memcpy(buf, field->name, field->name_length);
       buf[field->name_length] = 0;
-      colStr = rb_str_new2(buf);
+
 #ifdef HAVE_RUBY_ENCODING_H
-      rb_enc_associate(colStr, rb_utf8_encoding());
-#endif
+      rb_field = rb_intern3(buf, field->name_length, rb_utf8_encoding());
+      rb_field = ID2SYM(rb_field);
+#else
+      VALUE colStr;
+      colStr = rb_str_new2(buf);
       rb_field = ID2SYM(rb_to_id(colStr));
+#endif
     } else {
       rb_field = rb_str_new(field->name, field->name_length);
 #ifdef HAVE_RUBY_ENCODING_H