validation option ":if" is ignored

[bfolkens]

For the validates_length_of_password_field_options, validates_confirmation_of_password_field_options, and validates_length_of_password_confirmation_field_options the :if option is ignored. It appears that a merge is executed against the options hash, overwriting the :if option. Can we change this to a reverse_merge? http://gist.github.com/251422

(I wanted to run this against the test suite but I couldn't get the suite to pass regardless of this patch's presence)