The case fails on glsl2 branch (f8d2cfe4a699faebd42bd1874ef0329d37791dd7) with below output, and passes on master branch.
piglit/tests/fbo/fbo-drawbuffers-maxtargets.c:80: attach_texture: Assertion `glGetError() == 0' failed
This will be fixed as soon as loop unrolling is implemented. I'm working on that now.
Fixed by the following commit and the preceding commits in the glsl2-loops branch (now merged to master):
Author: Ian Romanick <firstname.lastname@example.org>
Date: Fri Aug 27 16:22:36 2010 -0700
glsl2: Allow copy / constant propagation into array indices