Fixed various bugs that surfaced in TPoX testing. - index maintenance must take into account that indexes for frequent   values are not stored; - access to ws_overlaps_ws must happen with short lock held.
Fixed various bugs that surfaced in TPoX testing.
- index maintenance must take into account that indexes for frequent
  values are not stored;
- access to ws_overlaps_ws must happen with short lock held.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb