Bugfix release v2.4.3

Fixed bugs:

• with_kw_args behaved differently on the v2.4 branch and on v3. The former would try to match the whole keyword arg hash with a matching object, the latter would iterate over the given keys. This release aligns the behavior of 2.4.3 with the one from 3.x. No changes on 3.x needed
• make sure flexmock works even with activesupport's definition of with on Object
• fixed some keyword argument forwarding issues