[Evolution-hackers] mail component api & other changes

[Not Zed <notzed ximian com>]

just fyi, i changed mail_component* functions to handle NULL passed as
the component to mean 'default component', which means you dont need
that fugly mail_component_peek() stuff everywhere anymore.

I'm actually pretty sure there's no need to have to pass the component
around anyway - there can be only one (tm), but that was enough change
to make at one time already.

I also removed default_*_folder_uri, and sent_folder/outbox_folder/
inbox_folder/etc, and you now need to go through
mail_component_get_folder() mail_component_get_folder_uri().  This is so
the local-store isn't initialised till it needs to be, so you don't get
empty inbox/etc folders setup, interfering with upgrade/first run
initialisation order.

A lot of changes, so hopefully it hasn't broken anything.

I also changed the shell startup order for upgrades, as per the previous
patch (JP said he'd tried something else but with no details I went
ahead anyway).