New C++ GDB PR category

[Elena Zannoni]

Andrew has gone mad (must be the lack of UV light in the grey north),
and added a bazillion categories to the GNATS database.

As an $ENDOFYEARFESTIVITY present to the c++ people, I went
through the pr's and moved all I could find related to C++ into the
C++ category.

I found 44 bug reports. Please, audit them, since some may have been
fixed or may be no longer pertinent.

Have fun.
Elena