These are replaced with
ctx->Const.Program[MESA_SHADER_{VERTEX,FRAGMENT,GEOMETRY}].  In
patches to follow, this will allow us to replace a lot of ad-hoc logic
with a variable index into the array.

With the exception of the changes to mtypes.h, this patch was
generated entirely by the command:

    find src -type f '(' -iname '*.c' -o -iname '*.cpp' -o -iname '*.py' \
    -o -iname '*.y' ')' -print0 | xargs -0 sed -i \
    -e 's/Const\.VertexProgram/Const.Program[MESA_SHADER_VERTEX]/g' \
    -e 's/Const\.GeometryProgram/Const.Program[MESA_SHADER_GEOMETRY]/g' \
    -e 's/Const\.FragmentProgram/Const.Program[MESA_SHADER_FRAGMENT]/g'

Suggested-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>