quakespasm 0.91.0

Version 0.91.0 of QuakeSpasm is released.
Changes since the previous version:

Bugfixes:

• Fix unwanted fog mode change upon video restart.
• Work around Intel 855 bug in status bar drawing with "r_oldwater 0"
  and "scr_sbaralpha 0".
• Fix an obscure GLSL bug where changing gamma would result in the
  screen turning to noise.
• Fix GLSL gamma causing the tiled screen border to turn white when
  "sizedown" is used.
• Fix an alias model VBO renderer bug where a model not precached
  during map start wouldn't be drawn.
• Fix the order of OpenGL context creation and window creation in
  SDL2 video.
• Fix a calling convention issue in windows DPI awareness function
  pointers.
• Fix a random texture recoloring after video mode change.
• Fix a liquid turning to garbage after several video mode changes
  and "r_oldwater 0".
• Fix a wrong alpha-sorting bug introduced in 0.90.1.
• Fix "flush" command not reloading mdl's from disk (bug introduced
  in 0.90.1).
• Prevent a possible buffer overflow in Cbuf_Execute (old Q1/Q2 bug).
• Prevent a possible vulnerability in MSG_ReadString (old Q1/Q2 bug).

Visual improvements:

• New cvars r_lavaalpha, r_slimealpha, r_telealpha for fine-tuning
  specific liquid opacities (from DirectQ/RMQEngine, non-archived,
  default to 0), and new worldspawn keys _wateralpha, _lavaalpha,
  _slimealpha, _telealpha, _skyfog (unique to Quakespasm, similar to
  the behaviour of the "fog" worldspawn key).
• GLSL gamma is now supported on older hardware without NPOT
  extension.

Interface improvements:

• New r_pos command to show player position.
• NaN detection in traceline with "developer 1" set now warns instead
  of errors.

Code cleanup / Other:

• Update third-party libraries.

Raised limits:

• Default max_edicts 8192 (was 2048) and no longer saved to config.cfg.
• Default heapsize 256 MB (was 64 MB).
• Default zone 4 MB (was 384 KB).
• Raised MAX_SFX to 1024 (was 512).