Add rock-find-root and rock-source-env shell helpers

[2maz]

This adds shell functions to facilitate sourcing the env.sh when working with multiple projects on the same machine: 'rock-source-env' crawls the directory hierarchy backwards to find and source the currently relevant env.sh

Pls do not merge yet, just comment.

[doudou]

Isn't that aenv here: https://rock.opendfki.de/wiki/WikiStart/Toolchain/MultipleInstalls

Nothing against it per se. The only reason aenv stayed outside of this file is that you obviously can't use the helpers from this file before you sourced the first env.sh

[2maz]

Ok, seems I missed or forgot about that -- one more reason I see to embed the code into autoproj or base/script.
Though there is a slight difference still. I like to avoid the autoloading part, i.e. requiring still to call aenv or similar in the shell.

[doudou]

Ok, seems I missed or forgot about that -- one more reason I see to embed the code into autoproj or base/script.

The problem is that you can't have it available - even if in base/scripts - before you sourced env.sh. It's a chicken-and-egg problem.

Generally speaking, if you find a good workflow around this, I think it would be very welcome in autoproj - I don't see the reason to put it inside Rock-specific stuff.