[Mesa-dev] arb_shader_subroutine CTS fixes

[Dave Airlie]

Since I wrote ARB_shader_subroutine as mostly a hack to enable GL4.0,
I felt a bit guilty and looked at CTS issues with it.

There are a bunch of CTS tests that do explicit location/index with
subroutines that were broken, along with a fair few of the subroutine
tests.

This is my first pass set of patches, there is still work to be done,
but these should all fix things now.

The big remaining ugly is that subroutines assignments are meant to
be per context not per program, and I haven't gotten to fixing that yet.

Dave.