Import soil-20080707 as wip/soil.

SOIL is a tiny C library used primarily for uploading textures into OpenGL. It
is based on stb_image version 1.16, the public domain code from Sean Barrett. It
has been extended to load TGA and DDS files, and to perform common functions
needed in loading OpenGL textures. SOIL can also be used to save and load images
in a variety of formats (useful for loading height maps, non-OpenGL
applications, etc.).
+soil
Rename MESSAGES to MESSAGE.