Fixes ctran/annotate_models#173, by ensuring that the model is coerced to a string before it's run through `ActiveSupport::Inflector.underscore`, which then correctly compares to the filename (which is a string already).

This reverts commit b11928ed.

the special-purpose file resolution method for test/spec files was failing
with namespaced test files (ex. User model attributes would annotate both
test/unit/user_test.rb as well as test/unit/foo/user_test.rb, instead of
only the former)

if column limit is an array, the values are serialilzed into column attr
  cf enum_column3 gem

restore PR#50 - see https://github.com/ctran/annotate_models/commit/cfeec96c9ca0fa5035b10be3d73e798cc4fc52f7