Change imap copy/save and trash to sync flags, excluding deleted. (closes #3966)...

Change imap copy/save and trash to sync flags, excluding deleted. (closes #3966) (closes #3860)

imap_copy_messages() uses a helper to sync the flags before performing
a server-side copy.  However, it had a bug that the "deleted" flag on
a local message, if set, will be propagated to the copy too.

Change the copy sync helper to ignore the deleted flag.  Then, change
the imap trash function to use the same helper.

Thanks to Anton Lindqvist for his excellent bug report, suggested
fixes, and help testing.