Description of issue or feature request:
Fix in accordance with #957 (and #963)!!

The repository tool's delegate_hashed_bins creates hash bins (delegated targets roles) and assigns passed target file paths based on their hash. Later it calls delegate for each bin passing the relevant paths. delegate then might left-strip the targets directory path from each targets path, changing the targets path in a way that it no longer is in the right bin.

Current behavior:
delegate_hashed_bins might hash target path based on a different path than the one that will appear in the (delegated) targets metadata.

Expected behavior:
delegate_hashed_bins must hash a target path as it appears in metadata.