matrix import - sparse matrix format should import GDM format

[GoogleCodeExporter]

Changes under issue 82 supported the import of sparse matrices (tables where 
there is one value per row).

These do no support cases where a GDM style format is used and the element ID 
is divided across multiple columns. e.g.:
x1,y1,x2,y2,val

Original issue reported on code.google.com by shawnlaffan on 3 Nov 2014 at 9:40