Support for the size attribute in TnyHeader

[Philip Van Hoof <spam pvanhoof be>]

I added support for the size attribute in TnyHeader. The API goes like
this:

guint tny_header_get_message_size (TnyHeader *header)

It works on both POP and IMAP and on newly written headers, once they
have been put in a TnyMsg, too (or, should .. but please test this new
functionality. It's a candidate for a nice unit test).

This is in preparation for a size-limited retrieval strategy (which is
different from partial retrieval in that it limits on message size).


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