Test build: effects turning black after a long session (#30)

Test build for #30. Not a release: the launcher does not offer it as an update. It is 0.51-linux.19 plus one change.

Effects turning black after a long session (#30). On NVIDIA and Intel the port keeps copies of the game's memory in video memory, and they only left it when the driver said video memory was nearly full, which an 8 GB card never reached. In an hour they grew from 64 MiB to 1.8 GiB. The texture cache counts them but can only free textures, so it reached its critical mark and started freeing textures the GPU had drawn, which is when the black effects show up. Now the copies nobody used for 30 seconds leave video memory first, as soon as the cache gets near its critical mark.

What would help: play as usual for a long session, with lamp travels, and attach the log in #30 whether or not the black effects come back (Advanced → Developer → Save the log and statistics to a file; it goes to ~/.local/share/bbport/logs).

SHA-256: 96628bdbadc1b27eb47050157badbafe6ff06ee6402479c3c0607bd039867b8b

Includes Lantern Engine by Awaken (https://github.com/Awakenchan/LanternEngine).