region: Enable or disable fatal errors and selfchecks based on version number
There is a couple of bugs in bugzilla where bugs in the X server
triggered asserts in the pixman region code. It is probably better to
let the X server survive this. (In fact, I thought I had disabled them
for 0.16.0, but apparently not).
The patch below uses these rules:
- In _stable_ pixman releases, assertions and selfchecks are turned
off. Assertions, so that the X server doesn't die. Selfchecks,
for performance reasons.
- In _unstable_ pixman releases, both assertions and selfcheck are
turned on. These releases are what get added to development
distributions such as rawhide, so we want as much self-checking
as possible.
- In _random git checkouts_, assertions are enabled, so that bugs
are caught, but selfchecks are disabled so that you can use them
for performance work without having to fiddle with turning
selfchecks off.