* Added the operation cancel_all_operations to the progress objects

	* The cancel button now invokes the cancel_all operation
	* Fixed modest_mail_operation cancel, now it really calls tny_account_cancel
	* Removed the ugly did_a_cancel static boolean in the mail operations
	* Fixed a leak with the new headers received when doing a send&receive
	* Fixes NB#62946, several clicks on cancel do not make the application crash when S&R
	* Fixed the new_headers count that was returned by the update_account_thread, it was wrong and was returning always 0 because the new_headers were freed before

pmo-trunk-r2735