Ignore any unused entry that starts with '_'.

This makes it possible to follow PEP8 which recommends '__',
and to name unused entries, e.g.:

    foo, _bar, _zed = func()
Fix caching issues of cython magic.

Should fix https://github.com/ipython/ipython/issues/6507 when using cython magic. 
We will deprecate cython magic in IPython itself.
Merge pull request #322 from Carreau/patch-1

Fix caching issues of cython magic.
add missing declarations for slice C-API
remove unused import
changelog
extract sys_time.pxd from time.pxd to fix naming collision of "struct timezone" and "long timezone"
split posix time tests in the same way as posix/time.pxd file before
remove unused text from test
make Py_hash_t a known type
expand section on cython -a output

* explain new "+" signs in front of lines
* explain different shades of yellow
* relation to nogil blocks
Merge pull request #323 from larsmans/annotation-docs

expand doc section on cython -a output
fix some typos

--HG--
extra : transplant_source : u%8C%DA%B6W%85%BC%FDA%A0%9C8%B6%16%86B%12%B6%1C/
fix broken name reference (probably after an incomplete refactoring)

--HG--
extra : transplant_source : %5ET%93%08%03d%EFC%C5X%D7%03%28%C4%EF%1DO%CC%1A%7C
fix up demo code

--HG--
extra : transplant_source : %FF%0B%A3%9D%21%85%A9%1A%8B%D1V%AD%CF%DD%3Em%92%DE_%8F
minor code cleanup

--HG--
extra : transplant_source : %C6f%B9L%06%0A%97m%15K%F7%CCN%90%B0%A5%90%04%96%A9
minor code cleanup

--HG--
extra : transplant_source : 8wv%A8%80%0B%7D%CA7%C8%10%B7%E4-I%F4%D0%29%D7%CC
fix up example code

--HG--
extra : transplant_source : %CA%C1%8A%A1%D8g%1C%B1%00R%CA%C2%09%11%08%CE%60IG%1A
remove compatibility #define for PyMethod_New() as it breaks the macro definition

--HG--
extra : transplant_source : V%1D%AF%BB%C2%E7l4%28%AE%8C%A9-%B0%B4%11%91%1B%FB%2C
restrict Jedi tests to Jedi 0.8.1 and later

--HG--
extra : transplant_source : %CC%5B%1C%85Jy%96%C2%29%CDt%26%E0W%EB%0C8%DF%0Fb