Initial implementation of MESA_texture_array

Shadow sampling from texture arrays is still not implemented.  Everything
else should be there, though.

src/mesa/main/state.c

@@ -812,6 +812,11 @@ _mesa_init_exec_table(struct _glapi_table *exec)
    SET_ProgramEnvParameters4fvEXT(exec, _mesa_ProgramEnvParameters4fvEXT);
    SET_ProgramLocalParameters4fvEXT(exec, _mesa_ProgramLocalParameters4fvEXT);
 #endif
+
+   /* GL_MESA_texture_array / GL_EXT_texture_array */
+#if FEATURE_EXT_framebuffer_object
+   SET_FramebufferTextureLayerEXT(exec, _mesa_FramebufferTextureLayerEXT);
+#endif
 }