error at rename attribute column

[zonky2]

error at rename attribute column e.g. Test to test

An exception occurred while executing 'ALTER TABLE mm_employees ADD test varchar(255) NOT NULL default ''': SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'test'

relatet to #1265

[discordier]

We should keep an eye on this one if #1267 also fixes this.

[zonky2]

the column names are not case-sensitive on Windows - see https://dev.mysql.com/doc/refman/5.6/en/identifier-case-sensitivity.html

But in MM 2.3 (MM 2.2?) we have a human readable error message