Added support for newsyslog.

Newsyslog
(http://www.freebsd.org/cgi/man.cgi?query=newsyslog&sektion=8) used on
FreeBSD and Mac OS X has the option to compress using bzip2.

It also starts it number suffix at 0 instead of at 1 like logrotate.

Added a check for the existing of a .bz2 extension in
`syslog-previous-file` and added a configurable start number for
rotation number suffix (`syslog-number-suffix-start`).
Merge pull request #2 from arnested/newsyslog

Added support for newsyslog.