kconfiggroup do not #include <QDir> twice

Fix krazy issue "Check for proper include directives [includes]... 1 issue found
~/kde/src/kconfig/src/core/kconfiggroup.cpp: duplicate includes line#20,393(QDir)
Use <..> to include installed headers; cpp file should include
their own headers first (but below config.h); other rules apply,
see
<http://community.kde.org/Policies/Library_Code_Policy#Getting_.23i
ncludes_right>. Use include guards in headers with appropriately
encoded macro names.".