In 5eab9df0df, I updated the
outputFileStamps task to compute all of the stamps for a directory
recursively if an output file is a directory. Prior to that, it had only
computed the stamp for the directory itself. This caused a significant
performance regression in creating the test classloader because it was
computing the last modified time for all of the classfiles in the class path.
The test for 5000 source files in
https://github.com/eatkins/scala-build-watch-performance was running roughly
400ms slower due to this regression.