Improvements to cython-mode.el

remove another reference to the old distutils build (in quickstart!) and clarify the description of the Sage notebook a bit

--HG--
extra : transplant_source : %B0%FFOZ%A1%AE%0F%18%A1%D9N%15W%11%5C%60%5E%02%FD%E6

fix glitch in dict.keys/values/items() optimisation for subtype calls under Python 3: called object method instead of supertype method

--HG--
extra : transplant_source : %94%87%D7e%B9%82%EF%926%26o%C0%8E%0DcY%C3%E3n%DB

--HG--
extra : rebase_source : 562b717b9c1e078b3f83e3febc8addc1a29d85fe

Update pyximport.py

this should be changed