leg: don't validate the presence of upgraded field

From http://stackoverflow.com/questions/5219150/problem-with-passing-booleans-to-update-attributes:

There's little point validating the presence of a boolean flag - it's going to be true, nil or false
and in Ruby world, nil and false have the same semantic value when it comes to boolean logic.

Internally, validates :presence relies on the value of the attribute being checked to return false when blank?
is called. And, in Rails (with ActiveSupport), false.blank? evaluates as true - which means that your field is failing the validation.

Signed-off-by: diditclear <didyourupgradeclear@gmail.com>