mesa: Rename ElementArrayBufferObj to IndexBufferObj.

mesa: Rename ElementArrayBufferObj to IndexBufferObj.

DirectX and most hardware documentation use the term "Index Buffer" to
refer to a buffer containing indexes into arrays of vertex data, which
allows random access to vertex data, rather than sequential access.

OpenGL uses a different term for this concept: "Element Array Buffer".
However, "Index Buffer" has become much more widespread.  A quick
Google search shows 29,300 hits for "Element Array Buffer" vs.
82,300 hits for "Index Buffer."

Arguably, "Index Buffer" is clearer: an "element of an array" (or list)
usually refers to an actual item stored in the array, not the index used
to refer to it.

The terminology is also already used in Mesa: some VBO module code for
dealing with ElementArrayBufferObj names local variables "ib".

Completely generated by:
$ find . -type f -print0 | xargs -0 sed -i \
  's/ElementArrayBufferObj/IndexBufferObj/g'

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>