use optimised dict iteration also for untyped objects when the known iterkeys/values/items() methods are used

--HG--
extra : transplant_source : %FAOM%F4%BF%9E%B68%F0%E6%A2%C8P4sz%F4%B7%DBG

--HG--
extra : transplant_source : %E3%97%5E9%1A%97%9BR%EC%01%FD%A0%B7-%81%C5G%AD%DA%DC

--HG--
extra : transplant_source : %21G%91%9Cy%EB%90%1Al%06%13%3B%C0%CB%0D%10%068%DC%E9

--HG--
extra : transplant_source : %E8%28%A4n%05%B9Q%7E%BBXuXn%21f%05c%60%5B%AB

--HG--
extra : transplant_source : %04E%21%DB%F8%D4%C0%FD%C7%11%5E%F1%28%C6%26R%E9%06%CE%FD

--HG--
extra : transplant_source : GI%ADU%5E%CEId%CET6%90%8D%F8%AB%CCr%3FCy

--HG--
extra : transplant_source : %EF%CB8%5D%B9%20%C4%9E%D9%BC8%BD%D9w4%AA%ABk%0B%EB

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

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

--HG--
extra : transplant_source : %AE%FF9%0ALO%CE%5E%C7%93%FA%B1d%E73%E8%CA%BE%DC%C8

--HG--
extra : transplant_source : %B2Q%A0%A7c%3B%EE%40%93%08%E1%C9-%83%88%BA%ACU%7D%8D

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

--HG--
extra : transplant_source : J%FF%93%9C%96%02%E8m%0E%AD7V%A5%1C%CF%7D%89%F6%14J

--HG--
extra : transplant_source : %D9%C4%E5%B7%FC9%0D%60%80R%E2%87%82S%9D%9C%8Bd%C3%C5

--HG--
extra : transplant_source : 8%3D%9FB%EA%E9%08%0A%7B%CB%92%ED%89%ADzL%9Du6%E9

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

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

--HG--
extra : transplant_source : m%879%8BW%7D%87%87%F5oYoA%ABl%88I%EF%92%FA

--HG--
extra : transplant_source : n%98%20%EE%A3N%1D%20%3F%88%2A%8B%FE%A0%01%97%9F%04%ED%23

--HG--
extra : transplant_source : fE%C2RT%7EHt%958%F4%257o%00%CB%3B%C3%B7%BA

fixed unused function warning about __pyx_clear_code_object_cache() when cleanup code is not being generated

libcpp.string supports s[0]= and s.at(0)=