Ensure that libcaf.h is early in includes
Ensure that libcaf.h is early in includes

 May fix #388 (issue with Clang 4 on FreeBSD)

sourceryinstitute/opencoarrays,sourceryinstitute/opencoarrays,zbeekman/opencoarrays,zbeekman/opencoarrays,zbeekman/opencoarrays,sourceryinstitute/opencoarrays