faster subject/sender/date sorting

[maf@tkrat.org]

On  7 Apr, laurent.duperval@microcell.ca wrote:
> FWIW, I find that sending email has now become much slower than it used to
> be (before there was the Outgoing folder). It seems like sending copies to
> the outgoing folder then waits for the initial conversation with the SMTP
> server is completed before control is given back to the user. I'm hoping
> that your first patch will correct this.

Unfortunately it will not speed up sending. I'll see what I can do about
the sending speed.

	/MaF