Non-termination for directory reduction containing dynamically created files

[Esben Sparre Andreasen]

The current implementation of delta_multi.js finds a fix-point for the shasum of the reduced target directory. That process does not terminate if the target program dynamically generates new files in the target directory, since the new files will change the shasum!

Solution: let all reduction steps return true/false based on their success. The fixpoint is reached if they all return false during one fixpoint iteration. (this should also be faster since the shasum computation is avoided)