Increase number of items for which list.extend([...]) is optimised. Benchmarking shows that append() is still faster for 8 items (on an empty list) than extend().
This limit could be increased for larger lists (which grow by a larger amount), but if we have to settle on one value then 8 is good enough, as we can expect literal item lists to be rather short.

cleanup and simplification, moved some optimised builtin list methods into the transform to see how it works out

tons of fixes for the test suite: docstrings must be unicode strings to run in Py3's doctest (obviously...)

--HG--
rename : tests/compile/withnogil.pyx => tests/run/withnogil.pyx