Problem: "SELECT INTO OUTFILE" created incorrect dumps for BLOBs,
so "LOAD DATA" later incorrectly interpreted 0x5C as the second
byte of a multi-byte sequence, instead of escape character.
Fix: adding escaping of multi-byte heads.


mysql-test/r/ctype_big5.result:
  Adding test case
mysql-test/t/ctype_big5.test:
  Adding test case
sql/sql_class.cc:
  Add escape characters before multi-byte heads.
strings/ctype-big5.c:
  Flagging character set as dangerous for escaping.
strings/ctype-gbk.c:
  Flagging character set as dangerous for escaping.
strings/ctype-sjis.c:
  Flagging character set as dangerous for escaping.