Log Message:
net/ocsync: Install manpages into ${PKGMANDIR}.

This project uses CMake to configure the software.  Force the
manpages to be installed into ${CMAKE_INSTALL_MANDIR}, which is
defined by the included GNUInstallDirs CMake module.  The correct
environment variables are passed so that ${CMAKE_INSTALL_MANDIR}
points into ${PKGMANDIR}.