Use O_CLOEXEC and O_NONBLOCK from the os module

Instead of hard-coding them. It turns out they are
architecture-specific.

What we really want are `IN_CLOEXEC` and `IN_NONBLOCK`, but they appear
to be identical to the constants in the `os` module, the `IN_*`
constants are not available through the interpreter, and we don't want
to have to parse C header files to get them.

Addresses an issue raised in the discussion thread for chrisjbillington#20

inotify_simple.py

@@ -1,5 +1,5 @@
 from sys import version_info, getfilesystemencoding
-from os import strerror, read
+import os
 from enum import Enum, IntEnum
 from collections import namedtuple
 from struct import unpack_from, calcsize
@@ -36,7 +36,7 @@ def _libc_call(function, *args):
             return rc
         errno = get_errno()
         if errno != EINTR:
-            raise OSError(errno, strerror(errno))
+            raise OSError(errno, os.strerror(errno))
 
 
 #: A ``namedtuple`` (wd, mask, cookie, name) for an inotify event. On Python 3 the
@@ -47,9 +47,6 @@ def _libc_call(function, *args):
 _EVENT_FMT = 'iIII'
 _EVENT_SIZE = calcsize(_EVENT_FMT)
 
-CLOEXEC = 0o2000000
-NONBLOCK = 0o0004000
-
 
 class INotify(FileIO):
 
@@ -72,7 +69,9 @@ def __init__(self, inheritable=False, nonblocking=False):
                 child processes. The default,``False``, corresponds to passing the
                 ``IN_CLOEXEC`` flag to ``inotify_init1()``. Setting this flag when
                 opening filedescriptors is the default behaviour of Python standard
-                library functions since PEP 446.
+                library functions since PEP 446. On Python < 3.3, the file descriptor
+                will be inheritable and this argument has no effect, one must instead
+                use fcntl to set FD_CLOEXEC to make it non-inheritable.
 
             nonblocking (bool): whether to open the inotify file descriptor in
                 nonblocking mode, corresponding to passing the ``IN_NONBLOCK`` flag to
@@ -83,7 +82,8 @@ def __init__(self, inheritable=False, nonblocking=False):
                 manually with ``os.read(fd)``) to raise ``BlockingIOError`` if no data
                 is available."""
         global _libc; _libc = _libc or CDLL(find_library('c'), use_errno=True)
-        flags = (not inheritable) * CLOEXEC | bool(nonblocking) * NONBLOCK 
+        O_CLOEXEC = getattr(os, 'O_CLOEXEC', 0) # Only defined in Python 3.3+
+        flags = (not inheritable) * O_CLOEXEC | bool(nonblocking) * os.O_NONBLOCK 
         FileIO.__init__(self, _libc_call(_libc.inotify_init1, flags), mode='rb')
         self._poller = poll()
         self._poller.register(self.fileno())
@@ -152,7 +152,7 @@ def _readall(self):
         ioctl(self, FIONREAD, bytes_avail)
         if not bytes_avail.value:
             return b''
-        return read(self.fileno(), bytes_avail.value)
+        return os.read(self.fileno(), bytes_avail.value)
 
 
 def parse_events(data):