set CMake policies CMP0026 and CMP0048 to OLD

this is required for CMake 3.0 to stop it complaining that we access
the LOCATION target property and set the *_VERSION_* variables ourselves.
Merge pull request #659 from OPM/fix_cmake_3_0_warnings

set CMake policies CMP0026 and CMP0048 to OLD
Merge remote-tracking branch 'upstream/master'