* update INSTALL.cmake
* update INSTALL.MacOSX
* update autoconf
-see also lib/RELEASE-NOTES
* update cmake
* check whether development/autotests/keytest.py really needs QT4
investigate references to Qt4 in keytest
!!Changes with respect to external programs and libraries in 2.4:
* The Qt5 libraries are now used by default. In order to link against
- Qt4 the configure option --disable-qt5 has to be used.
+ Qt6 the configure option --enable-qt6 has to be used. Qt4 is not
+ supported anymore.
* The dependency on pplatex/dvipost was dropped.