Cannot switch from None/Blur to a shader or back

[Screwtapello]

I just got a bug report on Discord that I'm pasting here before it gets lost in scrollback:

There's some kind of bug in the OpenGL 3.2 driver, at least on BSD/Linux (GLX) where changing between an actual shader and the none/blur options breaks video until a program restart. It loads the shader or non-shader correctly on first start. Complains of a shader compilation error if you change it to a shader, or just goes to black video if you move away from one.

Apparently reinitialising the driver every time a shader is loaded fixes the problem (a big hammer), at the expense of flickering to black when shaders are changed.

[Screwtapello]

May be related to #85?