Bug 11843: prevent manual history from being overwritten if subscription switched...

Bug 11843: prevent manual history from being overwritten if subscription switched to automatic history

Test plan:
1/ Create a new subscription, with manual history enabled
2/ Edit history by clicking on "Edit history" under Planning tab (add
   some text)
3/ Receive some serials, see that received and missing issues are not
   updated in Summary tab
4/ Edit subscription and disable manual history
5/ Receive some serials, see that received and missing issues are
   updated, but your notes have been kept.
6/ Edit serials and change status from/to missing or not available.
   Check that missing issues are updated correctly.
7/ Edit serials and change status from/to arrived. Check that received
   issues are updated correctly.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>