Problem: for character sets having mbmaxlen==2,
  any ALTER TABLE changed TEXT column type to MEDIUMTEXT,
  due to wrong "internal length to create length" formula.
  Fix: removing rounding code introduced in early 4.1 time,
  which is not correct anymore.


mysql-test/r/ctype_gbk.result:
  Adding test case
mysql-test/t/ctype_gbk.test:
  Adding test case
sql/field.cc:
  Fixing "internal length to create length" formula.