Long custom field name in dropdown search builder

In search builder (and export) screen, the fields name are truncate if more than 13 characters. It cause 2 problems :

• it's impossible to distinguish between fields with the same label from different custom group
• grouping custom field from the same group can fail which make it even more difficult to find the proper field

We should either get rid of the 13 characters limit or let the user define the limit.