On WXGTK, drawing directly to the wxScreenDC outside a paint event doesn't seem to have an effect.
I suspect that MSWLogo drew directly to the screen instead of refreshing it because it was faster. In these cases, I don't expect it's noticably faster because a refresh should result in a BLIT from memory, which is roughly what the direct-to-screen logic was doing.
This change fixes a problem where the score, timing, and lives indicators weren't being rendered in Asteriod Miner on GNU/Linux.
