Quake 2 support improvements.

[m-x-d]

This adds support for several Quake 2 features, including area lights, palette and texture loading and transparent/sky/fence textures. Here's the list of notable changes:

Palette handling and loading:
The palette iteslf and palette handling functions were moved to the new imglib.cc file. LoadPalette function was added. For Quake 2, it will try to load the palette from pics/colormap.pcx and replace the palette with hardcoded Quake 2 palette if that fails. For Hexen 2, it will replace the palette with hardcoded Hexen 2 palette.

External texture loading:
Most of Quake 2 source ports can use true-color textures stored in conventional image formats. Several changes were made to support that in a generic manner:

• the new drgbatexdata property was added to mbsp_t. It's structured the same way as dtexdata and consists of dmiptexlump_t followed by new rgba_miptex_t structs, followed by image data stored as RGBA bytes. A new color_rgba struct was added to simplify image data handling.
• after loading the BSP, external textures are loaded into drgbatexdata (Quake 2, currently WAL and TGA images only), or converted from dtexdata (Quake / Hexen 2) (see LoadOrConvertTextures in imglib.cc).
• all image handling functions were changed to use rgba_miptex_t instead of miptex_t.

Surface lights:
This is not a direct port of qrad3 surface lights logic. Instead, it's a tweaked version of bouce light logic tuned to look similar to qrad3/arghrad3 surface lights (that's why there are some strange scalers here and there...). Lights setup is done in surflight.cc.

Other notable changes:

• SetQdirFromPath() was rewritten from scratch. Instead of searching for "quake" (or "quake2" in qrad3) folder in a given path, it searches for base game folder ("ID1" / "BASEQ2" / "DATA1"), which is more likely to be named exactly that. Also, basedir property was added. It stores the path to the base game folder (like "c:/Quake/id1/") (used in Q2 texture and palette loading logic to search for images in both base game and mod folders when those differ).
• "-arghradcompat" command line option was added. It converts some arghrad light properties to their ericw-tools equivalents (added for debugging reasons, so I don't have to keep and synchronize 2 versions of the same Q2 map to compare the results with argrad3/qrad3).
• Fixed, _project_texture: an extra row and column of pixels were drawn (most noticeable when using lores project_textures).
• Added, _project_texture: texture colors are now modulated by light color.
• Added, _project_texture: when "_project_texture" property is set and "mangle" / "_project_mangle" are not, projangle is set from "angles" property.
• .lit output is now enabled when _project_textures are used in the bsp.
• For Quake 2, cfg.rangescale now defaults to 1.0 to better match with argrad3/qrad3.
• Warning about delay/_falloff mismatch was moved to CheckEntityFields to avoid message spam.
• Bounce/surface lights counts are now displayed.
• All compilation warnings in "light" project were fixed.
• A couple of clang-suggested optimizations were implemented.
• Some consts were added here and there.
• Some variable names in function declarations were renamed to match with corresponding implementations.

[ericwa]

Wow, thanks, this looks great! Only had a quick look but will try to test it soon.

[ericwa]

Thanks again and sorry it took me so long to merge!

I made a couple of small edits, the main thing is the errors in SetQdirFromPath need to be non-fatal because I want to keep the ability to light Q1 bsp's outside of a Quake installation.