greater possibilities in extending KDecoration. KCommonDecoration
now does not inherit KDecoration, only wraps it (i.e. it's source
compatible). Added comments on how to extend KDecoration
in the future by subclassing to KDecoration2, added PORTING
document with all API changes in KDE4.
CCMAIL: kwin@kde.org
svn path=/trunk/KDE/kdebase/workspace/; revision=742976
