at least fix the crash when calling SdXImpressDocument::dispose for now

Can an experienced Impress developer please check the crash?

Change-Id: I84f532dde6aa61b997b949f6d7ef55026ced604c
add test for bnc#864396

Change-Id: I38d77a11acf6684cb583ba3e5ffb80f30f3f2fdc
disable this performance improvement

Somehow there is a bug. Might be an internal OPropertySet problem as I
can't find it in my new code.

Change-Id: I6658fa82f4158ef114baf80b8d9ed9ec44793d35