[Mesa-dev] Renderbuffer Get/Put hooks in core

[Eric Anholt]

In the process of enabling ARB_texture_float on intel, I realized that
the way we were doing renderbuffer accessors (GetRow, PutRow, and
friends) was rather silly -- there was one version in the core, and a
spantmp2.h version in the driver.  This moves some of our spans code
to using much easier-to-read functions in Mesa core, and fixes several
testcases along the way.