GL_TIMEOUT_IGNORED = 0xFFFFFFFFu would be incorrect.

It's used for https://www.opengl.org/sdk/docs/man3...glWaitSync.xml ,to specify the 64bit timeout parameter

Since ClanLib 3.1 (development git) requires c++#11, I guess we could use "enum class" for just that one.
or a "const unsigned long long GL_TIMEOUT_IGNORED" global

We try to avoid #defines, since they are not namespace friendly.