BVLC/caffe — pull request #471 by jeffdonahue (2014-06-03 06:55:34+00:00)
Title: Compile debug/release into separate directories

So you don't have to rebuild the whole thing to switch back and forth between debug and release builds. The `build` directory becomes a softlink which is updated (to the real build directory, either `.build_debug`, or `.build_release`) if the value of $DEBUG has changed.