Display both original value and mapped value when collapse_mapped_values is unset

[archaephyrryx]

The current behavior, when collapse_mapped_values in tree.rs in unset, is to show only the original value. In many cases, however, the mapped value is more semantically interesting to the end-user, as it may often be a bitwise interpretation of otherwise opaque subordinate values. We should show either the mapped value if the flag is set, or both otherwise.

(moved out of merged pr #109 for visibility)