[Evolution] spool folders

[Not Zed <notzed ximian com>]

I started the code for spool folders and committed some stuff.  It
passes some regression tests, but they dont really test interopation
with other clients, and no locking is even implemented yet.

So dont use it for anything important, you WILL lose mail.

You can't just yet anyway; you can create a spool file 'folder', but it
doesn't show up anywhere, and can't be opened from the gui yet; have to
work something out on how to make this happen (which hopefully isn't the
same awful hack used for local stores, sigh).

 !Z