ENUMs weren't allowed to have character 0xff, a perfectly good
character in some locales.  This was circumvented by mapping 0xff in
ENUMs to ',', thereby prevent actual commas from being used. Now if
0xff makes an appearance, we find a character not used in the enum and
use that as a separator. If no such character exists, we throw an
error.

Any solution would have broken some sort of existing behaviour. This
solution should serve both fractions (those with 0xff and those with
',' in their enums), but WILL REQUIRE A DUMP/RESTORE CYCLE FROM THOSE
WITH 0xff IN THEIR ENUMS. :-/ That is, mysqldump with their current
server, and restore when upgrading to one with this patch.


mysql-test/r/type_enum.result:
  Bug#24660: "enum" field type definition problem
  
  Show that enums can now contain NAMES_SEP_CHAR (0xff, which is a perfectly respectable
  char in some locales), or ',', or both.
mysql-test/t/type_enum.test:
  Bug#24660: "enum" field type definition problem
  
  Show that enums can now contain NAMES_SEP_CHAR (0xff, which is a perfectly respectable
  char in some locales), or ',', or both.
sql/table.cc:
  Bug#24660: "enum" field type definition problem
  
  Revert fix for Bug#20922.
sql/unireg.cc:
  Bug#24660: "enum" field type definition problem
  
  Use a field-separator for ENUM-values that is not part of those values. If impossible,
  throw error.