Commit b580eb2fb3 inadvertently caused the
man pages for symlinked BIND tools (named-compilezone, tsig-keygen) to
no longer be installed by "make install". Fix by restoring the commands
which ensure that.
Commit b580eb2fb3 inadvertently caused
dnstap-related man pages to be installed unconditionally. Ensure they
are only installed for dnstap-enabled builds.