In 0e6b3435a1, installation of the HTML manual
was accidentally dropped: setting install_dir on a custom_target only sets the
directory where something is going to be installed if it is installed at all,
but does not itself trigger installation. The latter has to be explicitly
requested, which is just what we do here to get the manual back.
Change-Id: Iff8b791de7e7cb4c8d747c2a9b1154b5fcc32fe0
Alois Wohlschlager
5df2cccc49
