MSVG rendering should report errors instead of failing silently

[toolforger]

MSVG rendering is known to be limited (the docs say so), but if MSVG hits a limitation, it should report an error or a warning instead of silently creating a faulty image.
The problem with the faulty image is that people won't know how to fix the problem, IM doesn't tell them. Judging by the number of search engine hits that explain how to fix this problem, I guess this is widespread enough of an issue that fixing it is worth the (possibly considerable) effort.

[toolforger]

Also reported on https://github.com/ImageMagick/ImageMagick/issues/46 .
See viewtopic.php?f=1&t=28416 for an SVG where you wouldn't want MSVG.