Issue #59 fixed. Log is now appended by default and logrotating is able
via SIGMINRT+10 signal.
Daemon mode is extended.

* .pid and .lock files are added to use with logrotate and other
external tools
* corresponding options is added to pgator startup options
* if pgator started with root previleges, try to drop them off when it
actually no need more. To do this pgator needs userid and groupid
specified in config (optional parameters).
Merge pull request #63 from DSoftOut/issue#59

Issue#59