[Clipart] Use 7Zip for the Open Cliparts distribution

[Glenn Randers-Pehrson <glennrp>]

Jonadab the Unsightly One wrote:
> I suspect that the bandwidth saved by
> our use of bzip2, for instance, is probably lost in the underflow,
> even though bzip2 is about ten times more widely deployed than 7Zip;
> it's still obscure, compared with the other formats.

Recent SourceForge statistics for libpng show about 20,200 tar.bz2
downloads
compared to 16,200 tar.gz and 12,700 zip.  It seems that bzip2 is
actually
making some inroads.

Glenn