This bug occurs when error message length exceeds allowed limit: my_error()
function outputs "%s" sequences instead of long string arguments.

Formats like %-.64s are very common in errmsg.txt files, however my_error()
function simply ignores precision of those formats.


mysys/my_error.c:
  Fixed bug #20710.
  This bug occurs when error message length exceeds allowed limit: my_error()
  function output "%s" sequences instead of long string arguments.
  my_error() function has been fixed to accept formats like %-.64s.
mysql-test/t/alter_table.test:
  Added test case for bug #20710.
mysql-test/r/alter_table.result:
  Added test case for bug #20710.