configure script on CentOS systems

When building PBS from source on CentOS systems, the configure script does not correctly parse the /etc/redhat-release reported version which causes it to fail.

This issue was observed on various developer CentOS systems when either using Mike's devbuild script or building --with-gsoap. Developers who build on CentOS and do not request --with-gsoap are unlikely to run into this issue, however it would affect a CentOS build if we were to have such a system in place. Ravi has confirmed that building on a CentOS 6.6 x53 system failed in this manner.