* Added a method to unregister a header in the window manager in case of error

	* Added a method to unregister a header in the window manager in case of error
	* Changed the way the information dialogs are shown, now they do not use gtk_dialog_run
	* Refactored the code that opens a message in the msg view window
	* Refactored the code that asks the user for a download approval
	* Reverted some changes in the modest_mail_operation_get_msg, the callback must be always called even in case of error
	* Modified all the modest_mail_operation_get_msg callbacks to handle properly errors in the mail operation

pmo-trunk-r2565