Fix 'phpmyadmin refuses to show tables with enums containing special data' bug #4380

Signed-off-by: Hugues Peccatte <hugues.peccatte@gmail.com>

Conflicts:
	ChangeLog
Use PMA_String class to substr multi-bytes.

Signed-off-by: Hugues Peccatte <hugues.peccatte@gmail.com>
Merge pull request #1159 from Tithugues/b4380_42

phpmyadmin refuses to show tables with enums containing special data