Support for VSD import
Submitted by Michael von Glasow
Currently, Dia has support for importing newer Vision .vdx files but not .vsd (binary) files generated with older versions of Visio.
A lot of work on VSD parsing has already been done in libvisio, which is used by LibreOffice (https://wiki.documentfoundation.org/DLP/Libraries/libvisio). It's under MPL 2.0, thus it should be compatible with the GPL2+ license of Dia.