it can mask legitimate EINVAL cases, causing busy loop

this reopens issue #148

core: allow 'callback' property of a watcher to be set to None; del .callback is no longer supported

This fixes links execution order to be the same as they were added, fixing issue #143
The microbenchmarks show that it's not slower, in fact, a bit faster.

subprocess: add 'timeout' parameter to wait() in Windows case to avoid raising TypeError (timeout is ignored on Windows for now)

Fix issue #150: Do not wait for write event in gevent.fileobject.SocketAdapter.sendall() if everything was written already. Based on patch by Mark Hingston.

disable test_signal.SiginterruptTest.test_without_siginterrupt and test_siginterrupt_on because they rely on os.read raising EINTR which gevent.os.read does not do

otherwise it does not seem to work inside parallels on a mounted directory

greentest.py: reimplement switch counting without relying on setUp/tearDown. disable switch counting for now since it more gets in a way than points out problems

move gevent.fileobject.ignore_errors into gevent.os.ignored_errors; do not call _map_errors where unnecessary; make gevent.os.read/write ignore EINTR (it's useless for gevent apps) and EINVAL on darwin (issue #148)

--HG--
rename : greentest/test_os.py => greentest/test__os.py

As a benign side-effect, if read or write is interrupted with EINTR, hub.wait() will be
called before calling read/write again. (previously read/write was called immediatelly)

thanks temoto!

commit.

This initial implementation contains cooperative read() and write(),
and also moves fork() from gevent.hub to gevent.os.