Fix OCE / OCC version detection.
reapply changes from 6f907c3b

avoiding to wrongly attribute the follwoing commit message to jobermayr

Thew previous commit detects the OCC/OCE version by parsing Standard_Version.hxx
using a REGEX. The result is saved as OCC_VERSION_STRING. The comparsion
VERSION_LESS requires cmake version >= 2.8.0