Bug #721286 - IMAPx: read messages become unread when reopening Evolution

Couple things changed here:

a) the camel_folder_summary_get_changed() could return list of changed
   messages only if they were loaded in memory, which is not correct - I
   think it's part of the issue why it failed

b) it could happen that imapx_server_sync_changes() was called to save some
   changes, but then didn't change anything; in such cases, messages marked
   as locally changed were never unmarked, which led to false tests; I added
   a function to unmark the messages as locally changed (this can cause slow
   close of evolution for the first time, due to unsetting of the flag, but
   later ends are fine)

c) state of the message flags on the server is the master state, except of
   the state where locally stored info is marked as locally changed. This
   allows to show proper state of messages on the server (it is influenced
   by a) and b) too, so it might take up to two evolution starts to get
   the same view in evolution as is the state on the server)

d) do not use CamelOperation in the parser thread, because it can be
   cancelled at an application end with camel_operation_cancel_all() call,
   which is done too early, before any pending jobs are properly finished
   (it can be IDLE job, or save of folder changes back to the server)