setup.py: make it PEP-8 compliant (break long line)
client, server: make PEP-8 clean, add __main__ check
client,config,server: refactor config reading code

There's now a wrapper class, NrpeConfig, that takes care of processing
defaults, reading config files and then merging them all together along
with command-line arguments. This produces an object that can easily be
inspected to obtain configuration information.

The ServerConfig class in server.py derives from NrpeConfig and adds the
parsing of command[] options.

This removes a good bit of duplication between client.py and server.py,
tidies things up generally and also brings in the start of SIGHUP config
reloading for the daemon.
defaults: turn allowed_hosts into an array

Now NrpeConfig can split comma-separated strings into arrays, use this
to split up allowed_hosts. We still don't do anything with it, mind...
http: rename nrpe_server variable to cfg

This is now passed the NrpeConfig object, so nrpe_server doesn't make
sense. It's also only used to obtain configuration information from.
propagate config reloads into NrpeHTTPServer

This allows the command list and dont_blame_nrpe to be updated using
SIGHUP.