Only enabled for software drivers at this point.

Note that the gl_buffer_object::Access enum field has been replaced by
a gl_buffer_object::AccessFlags bitfield.  The new field is a mask of
the GL_MAP_x_BIT flags which is a superset of the old GL_READ_ONLY,
GL_WRITE_ONLY and GL_READ_WRITE modes.  When we query GL_BUFFER_ACCESS_ARB
we translate the bitfield into the conventional enum values.

autoconf had been designating the 8 bit libOSMesa as the default
standalone osmesa, but the Makefile expected it to be linked to libGL.
Fix up the osmesa Makefile so that it allows any of the combinations of
standalone and channel width to be built.

Fixes bug #21980.

This is about a 30% performance win in OA with high settings on my GM45,
and experiments with 915GM indicate that it'll be around a 20% win there.
Currently, 915-class hardware is seriously hurt by the fact that we use
fence regs to control the tiling even for 3D instructions that could live
without them, so we spend a bunch of time waiting on previous rendering in
order to pull fences off.  Thus, the texture_tiling driconf option defaults
off there for now.

We're on the way to telling the kernel about when we need fence regs on our
objects or not, and this will cut the number of places needing them.

This prevents the width / height from being clipped to the window size before
the texture is allocated.  This matches intelCopyTexImage1D.

This should fix bug #21227

Signed-off-by: Ian Romanick <ian.romanick@intel.com>

This saves doing swtnl from uncached memory, which is painful.  Improves
clutter test-text performance by 10% since it started using VBOs.