This adds a GDK_DEBUG=default-settings flag which disables reads
from xsettings and Xft resources, and enables this for the testsuite.
This is one less way to get different testresults depending on the
environment. In particular, it was failing the css tests for me
due to getting the wrong font size because i have a different dpi.
:not() selectors cannot be radical because the bloomfilter only knows if
a value is set in any of the nodes, but cannot determine the opposite
(if a value is not set in at least one node), but that would be required
for:not() selectors.
However, this is very unlikely to happen in the real world, so it's not
worth optimizing.
Unfortunately, change tracking could know this, so by excluding the
:not() selectors from radical changes, the change tracking will now pick
them up. If that turns out to be a performance problem, we need to add a
special category for radical not filters, so change tracking and bloom
filters can deal with them.
The testcase demonstrating the problem in widget-factory has been
extrated and added.
