Switching the default for -fabi-version

[Benjamin Kosnik]

> Certainly I'd like to see whether -Wabi reports any warnings when
> building any of KDE (including Qt), the C++ parts of Gnome, OpenOffice,
> and Mozilla. 

It doesn't matter, but libstdc++ gets errors with -Wabi. It looks like
POOMA, and KDE do as well. 

>However, the KDE folks tell me that the first issue is
> getting 3.4 to build KDE at all; there appear to be many problems with
> stray semicolons that the new parser rejects.

Missing semicolons in member class declarations also have different
warning messages, and locations. For people who have gotten used to the
old messages, a bit of re-training is necessary.

-benjamin