* camel-folder.[ch]: Remove
	camel_folder_{get,free}_subfolder_info, as we want to be able to
	scan the whole subfolder tree without having to open any folders,
	so this needs to be in CamelStore. Remove can_hold_folders and
	can_hold_messages flags; things that don't hold messages are no
	longer considered CamelFolders.

	* camel-folder-summary.[ch]: Remove CamelFolderInfo stuff.

	* camel-store.[ch]: Add camel_store_{get,free}_folder_info, as
	well as camel_store_free_folder_info_full and ..._nop for default
	implementations, and camel_folder_info_free and
	camel_folder_info_build as convenience functions. Turn
	CamelFolderInfo into a tree structure and also add an "url"
	member.

	* providers/*/camel-*-folder.c: Remove subfolder_info and can_hold
	stuff.
	* providers/*/camel-*-store.c: Add folder_info stuff.

	* providers/imap/camel-imap-folder.c (imap_summary_free): Free the
	summary elements with camel_message_info_free, not
	camel_folder_info_free. Oops.

	* providers/imap/camel-imap-utils.c: const poison

svn path=/trunk/; revision=5663