Collaboration improvements

[stefanches7]

There is a problem with multiple people working on wBuild projects using version control systems, because the latter updates the modification date on pull.
Example: So say, Elegans updates a script and lets the build run overnight, then pulls it to git; Foraminifer comes tomorrow and pulls the changes, and although the very same script's output is already in the common folder, he has to run the whole build again, because modification date of the updated script is newer!

[stefanches7]

Ideas:

• Do some version control hack so that mod. date is preserved
• Use hashsums instead of modification date to check build's consistency