Don't force Hash::update to call to_hash unconditionally (fixes break…

…age with Devise 1.1.5)

Devise has a MonitoredHash class which implements #update and #to_hash
entirely reasonably as follows:

    def update(other_hash)
      other_hash.each_pair { |key, value| regular_writer(convert_key(key), value) }
      self
    end

    def to_hash; Hash.new.update(self) end

This causes an infinite recursion and subsequent stack overflow in the
presence of slim_scrooge's override of Hash#update.

We fix this by modifying slim_scrooge's override of that method to
only force #to_hash on instances of MonitoredHash

(See https://github.com/plataformatec/devise/blob/master/lib/devise/rails/warden_compat.rb#L60)

lib/slim_scrooge/monitored_hash.rb

@@ -87,17 +87,19 @@ def self._load(str)
   end
 end
 
-# We need to change the update method of Hash so that it *always* calls
-# to_hash.  This is because it normally checks if other_hash is a kind of
-# Hash, and doesn't bother calling to_hash if so.  But we need it to call
-# to_hash, because otherwise update will not get the complete columns
-# from a MonitoredHash
+# We need to change the update method of Hash so that it *always*
+# calls to_hash on MonitoredHash instances.  This is because it
+# normally checks if other_hash is a kind of Hash, and doesn't bother
+# calling to_hash if so.  But we need it to call to_hash, because
+# otherwise update will not get the complete columns from a
+# MonitoredHash
 #
 # This is not harmful - to_hash in a regular Hash just returns self.
 #
 class Hash
   alias_method :c_update, :update
   def update(other_hash, &block)
-    c_update(other_hash.to_hash, &block)
+    c_update(other_hash.is_a?(::SlimScrooge::MonitoredHash) ? other_hash.to_hash : other_hash,
+             &block)
   end
 end