* brushexport plugin fix: invert Y during YZ swap; invert V of UV coords (correct texturing)
* brushexport plugin: default to 'Don't collapse' option
q3map2: * obj export: save in popular 'Y = Up, -Z = Forward' format
* picomodel::obj: load as popular 'Y = Up, -Z = Forward' format
* picomodel::obj: fix support of back references in faces
Loading Wavefront OBJ models in picomodel (used by radiant and q3map2)
did not reset the surface vertex index when starting a new surface. This
caused there to be unused vertexes, equal to the number of vertexes in
all previous surfaces, at the beginning of each surface. Exponential OBJ
vertex memory usage as number of surfaces increases. It did not affect
displaying or processing the surface faces.
name w/o path: assume textures are in the folder, where model file is
absolute path or with ..: try to cut at "/models/" or "/textures/" (as if leading to game folders); do previous case, if not
strip extensions and turn slashes to forward ones anytime
* picomodel::obj: fix diffuse map paths loading from .mtl
There's a bug in picolib when parsing the first group in an .obj file.
The library tries to set the surface name to a surface pointer
that is still NULL.
This gets silently ignored but the problem reappears later
in a warning message when the material or a face is parsed.
