Cancel kinds, implicit and explicit

[Philip Van Hoof <spam pvanhoof be>]

Hey Hackers,

There's right now only one cancel, which happens either automatic and
implicit whenever you tny_folder_refresh_* (which happens implicit by
the folder-tree-model in libtinymailui-gtk) or explicit when you perform
a tny_account_cancel.

It would be better if this were two kinds of cancels and that certain
operations, like tny_folder_transfer_msgs_* don't subscribe as being a
automatic-cancellable, but only as a explicitly-cancellable.

Patches welcome, I might take a look at this myself soonish, so if you
plan to write the patch: ping me (so that we don't duplicate efforts).

-- 
Philip Van Hoof, freelance software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://pvanhoof.be/blog
http://codeminded.be