File paths containing "." cause export errors

[JoeOsborn]

I'm not sure that string splitting on "." here is the right move to get the file path without extension:

ob-latex-as-png/ob-latex-as-png.el

Line 107 in d21d436

(file (car (split-string file.ext "\\.")))

If I use a path like ../img/whatever.png the filename is just the empty string, which is not ideal. Locally I replaced this binding with (file-name-sans-extension file.ext) and it seems to work much better.