raster image of text-tref-01-b

Test viewer capability to handle a basic 'tref' element which points to a text string in an external file.

The test case consists of a single sub-test. The box in the middle of the frame should contain green "Simple external referenced text.", which is obtained by a 'tref' element reference to a 'text' element in a 'defs' section of another file (text-extTref-BE-18-targ.svg).

The rendered picture should match the reference image, except for possible variations in the text fonts and layout (per CSS2 rules).

The test also uses the 'rect' element, as well as basic fill (solid primary colors), stroke (black 1-pixel lines), font-family (Arial) and font-size properties.