mesa: Replace ctx->Shader.Current{Vertex,Fragment,Geometry}Program with an array.

These are replaced with
ctx->Shader.CurrentProgram[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' ')' \
    -print0 | xargs -0 sed -i \
    -e 's/\.CurrentVertexProgram/.CurrentProgram[MESA_SHADER_VERTEX]/g' \
    -e 's/\.CurrentGeometryProgram/.CurrentProgram[MESA_SHADER_GEOMETRY]/g' \
    -e 's/\.CurrentFragmentProgram/.CurrentProgram[MESA_SHADER_FRAGMENT]/g'

Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_cb_drawpixels.c

@@ -1364,7 +1364,7 @@ blit_copy_pixels(struct gl_context *ctx, GLint srcx, GLint srcy,
        !ctx->Stencil.Enabled &&
        !ctx->FragmentProgram.Enabled &&
        !ctx->VertexProgram.Enabled &&
-       !ctx->Shader.CurrentFragmentProgram &&
+       !ctx->Shader.CurrentProgram[MESA_SHADER_FRAGMENT] &&
        ctx->DrawBuffer->_NumColorDrawBuffers == 1 &&
        !ctx->Query.CondRenderQuery &&
        !ctx->Query.CurrentOcclusionObject) {