add more config file parsing; fix CONFIG.file pointing to av[0]

* fallback_root=s
* polling_intrval_ms=n
* sleep_after_disaster_ms=n

the format is
option=value # comment
without spaces around the equal sign, spaces after the value will be trimmed

at the moment polling_interval_ms can be reloaded on -HUP
if fallback_root is changed and then the config file
is reloaded, it will be ignored, because of the way
workers are initialized.

fixed issue where CONFIG.file was pointing to argv[0], which was rewritten by setproctitle