Provide access to original question and answer references.

Surveyor parses both of these forms equivalently:

    dependency :rule => "A"
    condition_A :foo, "==", :a_bar

    dependency :rule => "A"
    condition_A :q_foo, "==", :a_bar

Lunokhod handles both forms also, but prior to this commit, it did not
provide access to the original reference form.  (All you got was a
processed tag.)  This made it impossible to generate surveys from other
surveys whilst maintaining AST identity.

This commit introduces qref and aref readers to return the original
condition references.