First draft of logging functionality.

[David Bremner]

On Tue, 12 Oct 2010 11:06:17 +0200, Michal Sojka <sojkam1 at fel.cvut.cz> wrote:

> I'm not sure whether implementing logging facility outside of notmuch
> library is a good thing. If somebody will use a third-party tool (such
> as python bindings) to manipulate his tags, they won't appear in the
> log.

Yeah, thanks for that. I had been worrying about the same thing, but
your message helped clarify things for me.

I guess log files should be opened in notmuch_database_open, and the
actual logging in this case could happen from notmuch_message_add_tag.

>From an atomicity point of view it might make more sense to store up a
list of log lines, and dump them all from _notmuch_message_sync.
One could attach a log buffer to a message, and flush that atomically
when syncing the message back to the database. In this context, it is a
little more tedious to have more than one log file. 

d