add_nested_fields_for assumes partial's local variable is 'f'

[Paul Adams]

I have a partial that uses the local variable "form" instead of "f" which caused add_nested_fields_for to fail.

Changing my partial to use "f" fixed the failure, but forces code refactoring in other files.

[Jon Baker]

you are quite right, I will look into a fix. Thanks for spotting.