the previous version of operator*() made no sense. E.g., it violated the invariant
(*ptr).foo <=> ptr->foo. The dereferencing operator now returns a reference to the pointed-to
object, rather than a pointer to it.
I also added a bool conversion operator, which can be used in testing the NULL-ness of the
pointer. Anyone wondering if that could be done in a simpler way is encouraged to read
<http://www.artima.com/cppsource/safebool.html>.
And, finally, I removed the mutable flag from the m_data member, since it does not need it.
a 'BidiString' holds both the logical content and the visual reordered
version of the content of a string. this helps to reduce the number of
calls to reorder the string before drawing it (as introduced in the patch
from Ken Bloom) and to be more consistent in menus and textboxes (drawing
cursors and underlining text).
