The emulation of legacy RES_BACKGROUND properties claims that (unless
fillstyle is NONE) all of them are direct values, which causes export of
legacy attributes like style:background-transparency without
corresponding non-legacy draw:opacity.

Especially problematic for style:background-transparency, which is set
to 100% if style is bitmap, which is the reasonable default for API
backward compatibility of BackColorTransparency, but wrong for ODF.

Change-Id: I1fa4fa5df45eb00cbfcd2e171b4862c4e195cc7d