Reproduce the same functionality on fields

Other people seem to be looking for this function also on fields, so I thought I'd add what worked for me. I'm not a programmer so use at your own judgement.

See the attached files -- it's the same pattern as the base module, just modified for a field value (should be easy to follow the pattern for your field_name).

I have some extra validation in the unique.inc file - just delete it if you don't want it (remember to take out the call to the function higher up in the file too).

HUGE thank you to ardas for this module!