Don't require config file for supervisorctl

 * Adding require_configfile parameter to options.Options to be able to
   disable config file check for options.ClientOptions.
 * Refactored out searchpaths to become a member of options.Options.
   This made it possible to 1) test for the content of it and 2) disable
   automatic config file detection from within tests (and thus evade
   external side effects that might vary from developer to developer).
 * Adding an additional test of options.ServerOptions to make sure it
   still exits if it can't find a valid configuration file.

This is an initial commit that tries to fix issue #62.

All tests passes on my workstation. However, both `supervisord` and
`supervisorctl` crashed when executed. I will have to look into this.
Renamed `process_config_file()`

Renamed `process_config_file()` to `process_config()`.

The function does so much more than simply process the config file (such
as applying defaults). I also intend to factor out the code that does
not take care of parsing/reading the config file.

All tests pass on my local workstation.
Written a test that reproduces exception

The exception is thrown when

    $ supervisorctl

is executed in the terminal. This exception was the reason I withdrew
the pull request https://github.com/Supervisor/supervisor/pull/71.
Refactoring `Options.process_config()`

Moving a chunk of code out from `Options.process_config()` to
`Options.process_config_file()`. The latter function is now responsible
for only reading the config file while the former initializes config
data structure in general.

This commit makes it possible to skip the reading of an external
(on-disc) config file while still using default values etc.

The test `ControllerTests.test_real_controller_initialization(...)`
still fails because some default config values are not initialized
correctly. All other tests pass.
Fixing failing test

The test `ControllerTests.test_real_controller_initialization()` no
longer fails. This was fixed by making sure
`ClientOptions.plugin_factories` was initialized even though no
configuration file has been read.

All tests now (finally!) pass on my workstation.
Making sure that a test never finds a config file.

The intention of the test is that it is not supposed to find a config
file anywhere on-disc. My local workstation does not have one, but
future testers might.
Removing stdout test output

As per request by @mnaberez in pull request
https://github.com/Supervisor/supervisor/pull/95#issuecomment-10778589
Removing stderr output from test

As per request by @mnaberez in pull request
https://github.com/Supervisor/supervisor/pull/95#issuecomment-10778589
Merge pull request #95 from JensRantil/issue_62_pending2

Don't require config file for supervisorctl