Check for mounted /proc.
Clear only the requested range in gen6_ggtt_clear_range.

Sprinkle kasserts throughout i915_gem_gtt.c.
Tweak some DRM GEM page indexing crap.

- Fix order of subtraction in drm_mmap_paddr_locked.
- Address GEM objects' pages from 0, not from the mmap cookie.
- Check page alignment earlier in mmap code paths.
- Sprinkle kasserts throughout.

Still doesn't fix the garbage that is sometimes being scribbled all
over kernel memory!
Reduce a number of getsecs() calls in le_get() to make netboot a bit faster.
Add -fno-asynchronous-unwind-tables -fno-exceptions to gcc builds.
One of these (probably the first) is needed to stop the eh-frame
section being created.
The eh_frame section is loadable and bloats the boot images.
This might be enough to make pxeboot work.
Do not create debug info for *_INSTALL kernels.