optimise string-to-something comparisons also when we know that the result is boolean (the cmp functions have a proper fallback for non-strings)

revert dynamic tp_new() override because it breaks instantiating types with arguments that object.__new__()/object.__init__() don't expect

reuse object's tp_new() for simple extension types if possible to improve support for multiple inheritance

Special method docstring guard

--HG--
extra : amend_source : 95fc8a7afdf4614a3dfe7b9874d1ba8cd1bf9967

--HG--
extra : rebase_source : 22e9602b4fa5ddfd4e9577610afe1635b482a86d

be a little more relaxed about temping in assignments (looks like some things still can't be moved to a temp...)