Ok, last hurdle (I hope) for the CentOS migration:
If you get
Starting httpd: /usr/sbin/httpd: error while loading shared libraries: libpq.so.4: cannot open shared object file: No such file or directory
starting Apache2 on CentOS, possibly after having installed later versions of Postgresql and forcing some compat-postgresql-libs, you might proceed like this:
yum remove apr-util
(this will remove httpd / Apache2 also)
yum install httpd
(this will reinstall apr-util and [hopefully] fix the dependencies).
I got the hint from here, regarding the libpq dependencies:
John Schmidt: Great post. Fixed the issue.
marpen: good informations ..