Hub.shutdown: make sure current hub instance is not referenced by threadlocal variable even if it was never switched to

- if 'agressive' argument is true (default)

- because the original ImportError does not necessarily complain about greenlet,
  it may also complain about setuptools (No module named pkg_resources).

--HG--
extra : transplant_source : %0Ed%0B%01T%13%5DU0%C5%EF/%EC%A9%0D%A1%F1%E9%BDp

--HG--
extra : transplant_source : %C4%27%B3%96D%C3j%80%DE%FB%C3D%9A%CB%0F%A3%5D%CA%D5L

--HG--
extra : transplant_source : %13%A8fO%5Bt%8D%D6%5C%BC%8B%3B%BB%11%F2%DA%BC%13%04%8F

--HG--
extra : transplant_source : %ABb4%3F%065H%7D%2C%DC%B4L%FD%B7%FB%89%EAR.%83

--HG--
extra : transplant_source : %D8%1D%EAt%BBLJD%FB%1B%B9%1E%AF%7Co%A4%1D%5C%E7%CC

--HG--
extra : transplant_source : %A9P%8D%C3%D0%90%94lS%7E%A1%8B%B3%D8%BB%A94%9E4m

- short writes could force the server into a busy loop (i.e. basically a DOS attack)
- fix handling of trailing crlf when reading input with a length parameter
- fix handling of wsgi apps not consuming the whole input.
- make readline work with chunked input
- respect size parameter to readline method even if this isn't strictly required by the WSGI spec.

--HG--
extra : transplant_source : W%F8%B8y%C5_%83%C2%8B%1C%A6Ntn%8Bj%3F%29%86%04

--HG--
extra : transplant_source : %DB%FAZ%EE%1E%FA%93%E1%C1%1F%3C%B4G%1E%C2%0A%97%FD%E4K

--HG--
rename : greentest/test__switch_exc_info.py => greentest/test__exc_info.py