use %pre section of .rpm file to check if this package is already installed

[Dmytro Shyshchenko]

One rpm .spec file was developed long time ago and the %pre section of
it was used to check if a previous major version of this software is
already installed or not. And it did work before. I saw it personally.
In the rpm 4.8 (rhel 6.5-6.7), this does not work anymore. During
installation the rpm installer does not reach (or ignore?) the %pre
section and complains that "file ... from install of
our-software-23.01.el6.i386 conflicts with file from package
our-software-22.07.el6.i386" and then the installation aborts.

I have posted the same question also on the unix.stackexchange.com:
http://unix.stackexchange.com/questions/254883/pre-section-of-my-rpm-is-no-longer-executed-on-rhel-6-7

Is there a way to make it work or the check is supposed be done
different? Any help is much appreciated! Thank you in advance.