[FIX] Removes the limit of 64 characters from additional text fields added via the interface

[FIX] Removes the limit of 64 characters from additional text fields added via the interface

https://bugs.launchpad.net/openobject-server/+bug/1053511

This change is the same as done in:
http://bazaar.launchpad.net/~openerp-dev/openobject-server/7.0-opw-582876-cbi/revision/4908