Supressing cmake 3.0 policy warning for CMP0026

This change suppresses the cmake policy warning for policy CMP0026 emitted by cmake V3.0. The docs say that the old style

      get_target_property(<var> ${target} LOCATION)
 
should be replaced by using 

    $<TARGET_FILE> 

(see http://www.cmake.org/cmake/help/v3.0/policy/CMP0026.html). However it is not clear from the docs how this can be done.