Stéphane Marchesin, the founder of the Nouveau driver project that since moved on to working for Google on their Chrome OS team, committed to Mesa support for sRGB textures for this driver that targets the old i915 and i945 chipsets.
Google has been working on the i915g driver for use in Chrome OS by their original Chromebooks. They prefer the i915g driver to the i915 classic driver since the Gallium3D implementation can better emulate missing functionality using LLVM, etc. However, the i915g driver is now reaching a mature state and Google will lose interest in the driver as they turn to Sandy Bridge and Ivy Bridge for their Chromebooks. For the newer Intel hardware, Intel's Open-Source Technology Center remains committed to a "classic" Mesa DRI driver rather than Gallium3D and there is no community "G" alternative.
The Intel 915 hardware doesn't support sRGB textures so Marchesin's Mesa commit ends up emulating the textures using a shader. Thanks to the sRGB textures support, the i915g driver is now able to advertise OpenGL 2.1. However, Marchesin says, "I think this is as far as we can take the i915."
The sRGB textures are textures with standard RGB color-space encoded color components. This support has been part of the Khronos OpenGL specification since version 2.1 via the GL_EXT_texture_sRGB extension.