Render LaTeX PNGs on transparent background
Gajim renders LaTeX PNGs with the correct foreground color, but a static white background color. There are GTK themes that use a light foreground color on a dark background, so these users end up with white on white text, which isn't really user friendly (and thus violates Sections 1.1 and 8.1.2 besides many others of the Gnome Human Interface Guidelines[0], to support my case by formal references).
The trivial solution, as implemented by the attached patch, is to add '-bg Transparent' to the dvipng command line, causing dvipng to use a transparent background with correct antialiasing.