Provide a define for having OpenMP
Merge pull request #305 from rolk/305_openmp

Provide a define for having OpenMP
Merge remote-tracking branch 'upstream/master'
Enable support for Ninja build generator

Use the Ninja build generator if '--enable-ninja' is passed on the
command line to ./configure (or of course if -GNinja is passed
directly to CMake).
Merge pull request #306 from rolk/306_ninja

Enable support for Ninja build generator
Merge remote-tracking branch 'upstream/master'