support RLE+luminance+alpha tga files.
support half-float tga files.
recognise hdr astc images.
added appropriate fallbacks for astc support.
load mip-less .astc files (mostly just for debugging stuff).
allow packages to warn about required engine/gpu features.
catch when stdin flags get changed to blocking by external libraries, to avoid fatal stalls.
basic support for .mdx files (kingpin models)
sort packages loaded via wildcards, by datetime then name, to avoid random ordering from certain filesystems.
git-svn-id: https://svn.code.sf.net/p/fteqw/code/trunk@5531 fc73d0e0-1445-4013-8a0c-d673dee63da5
