modules: Do not count inserted/sent messages as stored ones.

Stored messages are for only queued messages inside syslog-ng.
Merge pull request #198 from talien/f/do-not-count-inserted-messages-as-stored

modules: Do not count inserted/sent messages as stored ones.

This also fixes #142.
lib/cfg.c: Increase the default flush_lines value

The default setting for flush_lines was 0, which meant different things
to different drivers, but was mostly equal to flush-lines(1).

This addresses the other part of #62.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>