enable-background is not parsed correctly
tests/fixtures/reftests/bugs/587721-text-transform.svg test has an
enable-background="new 0 0 1179.75118 687.74173" attribute in the toplevel
svg element. This fails to parse, because our parser for that property expects
new to not be followed by the dimensions of the background area. We need to support parsing them, at least. I don't know if the SVG spec specifies them as a hint only, or if they actually result in hard clipping for filters.
Relatedly, this is why
parse_style_attrs() ignores errors when parsing presentation attributes: if we don't ignore them, that
enable-background attribute causes that test to fail.