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This uses nagios' /usr/lib/nagios/plugins/check_http as packaged
within Debian.

"every" is a loop, meaning that it always has to rotate back to
the begining when the threshold is met. But retry is more like a
ceiling, menaning that after the threshold it is "too much".
So modulo is perfect for "every" and for "retry", use min().

Merge branch 'simpler-count-op' of http://gitlab.netlib.re/b4n/picomon into b4n/picomon-simpler-count-op

Split subprocess compatibility layers

Split subprocess_compat into several modules to make it easier to maintenance and extend.

Now, instead of having the threading fix in a class derived from the one enabling timeout support, have two classes both derived from subprocess.Popen, and merge them together at the package's root level:

```
               subprocess.Popen
              /                \
._timeout_popen.Popen    ._threaded_popen.Popen
                   \      /
                    .Popen
```

This completely splits up the timeout support and threading fixes, removing any dependency from one on the other, and allows to easily add or remove another compatibility class by simply adding or removing a parent class from the root Popen empty class.

Split subprocess_compat into several modules to make it easier to
maintenance and extend.

Now, instead of having the threading fix in a class derived from the
one enabling timeout support, have two classes both derived from
subprocess.Popen, and merge them together at the package's root level:

                         subprocess.Popen
                        /                \
          ._timeout_popen.Popen    ._threaded_popen.Popen
                             \      /
                              .Popen

This completely splits up the timeout support and threading fixes,
removing any dependency from one on the other, and allows to easily add
or remove another compatibility class by simply adding or removing a
parent class from the root Popen empty class.

Move workaround for Python bug http://bugs.python.org/issue18851 to
lib/subprocess_compat.py.

Continuous polling means that the process runs forever, checking
everything from time to time.
To get results, a listing of checks' state is printed when SIGUSR1
is caught. Single run (for config or debug) is accessible with the
-1 or --one command line switch.

Don't show empty outputs and decode bytes (so that things like newlines
are printed as such and not as litteral "\n").

The CheckDNSZone implementation now calls the check available here:
https://github.com/bortzmeyer/check_dns_soa

Handle OSError exceptions (such as non-existing command) for the
Popen command spawning.
Surround that by a mutex as Popen is not atomic when failing!

Create a directory "lib/", put the checks there. Move the compat file
there too.
Also put the config in a separate file so that users may edit without
messing up the core. Would also ease intallation so that config
may land in etc/ for example.

Apparently, Popen.args is new and undocumented in Python 3.3, so don't
rely on its existence and set it ourselves.

Now the granularity is the check level, allowing to write checks
without hosts. Checks don't deal with hosts anymore.
Also the results of checks are now handled outside of the checking
path, but this may change when the infinite loop and time intervals
are going to be implemented.

Conflicts:
	picomon.py

Subprocess Timeout

Adds support for timeout in subprocess communication for Python < 3.3, and use it in `Check.exec_with_timeout()`.

IPy is only used to get the version of an IP (4 or 6), but the IPs come
from reasonably trustable sources and if incorrect would at worse make
the test fail -- which is valid behavior.

So, no need for a real library to distinguish them, do a naive check
based on the presence of version-specific delimiters.

Pep8

Fix style to conform to PEP8