Fix KeyError if socket is removed in timer

[spaceone]

The following script demonstrates a KeyError which is caused if a socket which currently has some pending input/output was removed in a notifier timer.
The problem is that step() first poll()s, then executes the timers() and then uses the polled FD's.

$ cat timer_bug.py
import notifier
import subprocess
notifier.init()

fd = None
def on_read(sock):
        print 'on_read'
        return True
def on_timer():
        print 'on_timer'
        notifier.socket_remove(fd)
        return True
p = subprocess.Popen('python -c "import sys; sys.stdin.read()"', shell=True, stdin=subprocess.PIPE)
fd = p.stdin.fileno()
notifier.socket_add(fd, on_read)
notifier.timer_add(0, on_timer)
p.communicate('A')
notifier.step()

$ python timer_bug.py
on_timer
Traceback (most recent call last):
  File "timer_bug.py", line 18, in <module>
    notifier.step()
  File "/home/git/python-notifier/notifier/nf_generic.py", line 259, in step
    sock_obj = __sock_objects[ fd ]
KeyError: 4

[crunchy-github]

merged