frescobaldi-devel: remove subport name workaround

This is no longer needed, thanks to
https://trac.macports.org/ticket/40831
frescobaldi(-devel): check for ${dev_version} instead of subport name
frescobaldi(-devel): rename variable ${dev_version} -> ${devel_version}
frescobaldi-devel: upgrade to 20140727
README*.md: update version numbers