glsl: Rename uniform_field_visitor to program_resource_visitor.

There's actually nothing uniform-specific in uniform_field_visitor.
It is potentially useful for all kinds of program resources (in
particular, future patches will use it for transform feedback
varyings).

This patch renames it to program_resource_visitor, and clarifies
several comments, to reflect the fact that it is useful for more than
just uniforms.

NOTE: This is a candidate for the 9.1 branch.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/program/ir_to_mesa.cpp

@@ -2375,7 +2375,7 @@ print_program(struct prog_instruction *mesa_instructions,
    }
 }
 
-class add_uniform_to_shader : public uniform_field_visitor {
+class add_uniform_to_shader : public program_resource_visitor {
 public:
    add_uniform_to_shader(struct gl_shader_program *shader_program,
 			 struct gl_program_parameter_list *params)
@@ -2387,7 +2387,7 @@ public:
    void process(ir_variable *var)
    {
       this->idx = -1;
-      this->uniform_field_visitor::process(var);
+      this->program_resource_visitor::process(var);
 
       var->location = this->idx;
    }