buildbot: multiple failed dependencies reported as multiple broken builds in email report

[mojca (Mojca Miklavec)]

See ​this report:

Log from failed builds:
	Building 'root6' ... [ERROR] (failed to install dependency 'cmake')
	> maintainers: jonesc at hep.phy.cam.ac.uk,michaelld at macports.org,mojca at macports.org.
	Building 'root6' ... [ERROR] (failed to install dependency 'py27-setuptools')
	> maintainers: jmr at macports.org,jonesc at hep.phy.cam.ac.uk,mojca at macports.org.
	Building 'root6' ... [ERROR] (failed to install dependency 'harfbuzz')
	> maintainers: jonesc at hep.phy.cam.ac.uk,mojca at macports.org,ryandesign at macports.org.
	Building 'root6' ... [ERROR] (failed to install dependency 'libunwind')
	> maintainers: jeremyhu at macports.org,jonesc at hep.phy.cam.ac.uk,mojca at macports.org.
	Building 'root6' ... [ERROR] (failed to install dependency 'ocaml')
	> maintainers: jonesc at hep.phy.cam.ac.uk,mojca at macports.org,mww at macports.org.

that is generated by mpbb/mpbb-install-dependencies

        # $depvariants isn't quoted on purpose
        # shellcheck disable=SC2086
        if ! failcache_test "$depname" $depvariants; then
            text="Dependency '${depname}' with variants '${depvariants}' has previously failed and is required."
            echo "$text" >&2
            echo "$text" >> "$log_status_dependencies"
            echo "Building '$port' ... [ERROR] (failed to install dependency '${depname}') maintainers: $(get-maintainers "$port" "${depname}")." >> "$log_subports_progress"
            failcachecounter=$((failcachecounter + 1))
        fi

to result in ​this:

Building 'root6' ... [ERROR] (failed to install dependency 'cmake') maintainers: jonesc;hep.phy.cam.ac.uk,michaelld;macports.org,mojca;macports.org.
Building 'root6' ... [ERROR] (failed to install dependency 'py27-setuptools') maintainers: jmr;macports.org,jonesc;hep.phy.cam.ac.uk,mojca;macports.org.
Building 'root6' ... [ERROR] (failed to install dependency 'harfbuzz') maintainers: jonesc;hep.phy.cam.ac.uk,mojca;macports.org,ryandesign;macports.org.
Building 'root6' ... [ERROR] (failed to install dependency 'libunwind') maintainers: jeremyhu;macports.org,jonesc;hep.phy.cam.ac.uk,mojca;macports.org.
Building 'root6' ... [ERROR] (failed to install dependency 'ocaml') maintainers: jonesc;hep.phy.cam.ac.uk,mojca;macports.org,mww;macports.org.

and then converted to the email list inside master.cfg

It's harmless in principle and the list of recipients is correct, but the output should be improved. Suggestions welcome.