also use the fast optional kwargs lookup loop when we have **kwargs but receive less than the named optional kwargs

to help in breaking potential reference cycles, clear references in generator objects immediately on termination instead of waiting for them to be cleaned up

--HG--
extra : transplant_source : %28%90%91h.%EE%94%1AE%F5%A9%DA33J%D0%60h%F5t

--HG--
extra : transplant_source : %9F%0B%FF%0F%16%0C%25%B9%FA7%D8%25%9EDpJSE%5E%BB

--HG--
extra : transplant_source : %D5V%9A%D2%DE%A7%A8%20%21%05%FFp%DEk%C4f%3Ct%0DT

rewrite of dict iteration code at a more C-ish level in order to make the actual code C compile time dependent

--HG--
extra : transplant_source : R%BCF%17%5D%7E%FA%B3%C4q%D2%28%CF%0Di%8D%FC%0B%E4%7B

partial application of some PyPy related changes as far as they are uncontroversial and helpful for further utility code refactorings

--HG--
extra : transplant_source : %F8%87%C7%8B%90w%7E%8EG%04C%A9%89%9B%3E%FB%8CCp%F9