Fixed a bug where the copy constructor for SpecialCharTracker was
actually performing a shallow rather than a deep copy of the text
wrapper array. This meant that when the indices of text wrappers were
modified in the current taggedDoc, all taggedDocs on the undo stack
would also have their text wrapper indices modified, which could lead to
exceptions and other odd behavior when undoing after modifying text
inside a pair of text wrappers.