Provide a way to "fix" unspecified timestamps

[andreabedini]

In a workflow where a repository is updated by multiple people who submit PR or patches, a contributer is forced to specify a timestamp ahead of the time of merge. This implies the possbilty that patch A with timestamp t_A ends up being merged before patch B with timestamp t_B < t_A. In this case the repository, as built from the main branch, will experience a jump, breaking incremental updates and index-state semantics.

One possible way out is to defer fixing a timestamp to merge time. One could add timestamp where it's missing, just before the merge commit, e.g.

awk -i inplace '/timestamp = / { hasTimestamp = 1 }; !hasTimestamp { printf("timestamp = %s\n", strftime("%Y-%m-%dT%H:%M:%S", systime(), 1)) }; { print }' _sources/*/*/meta.toml

It would be nice if foliage could do this itself. At build time, meta.toml files missing the timestamp could optionally get a timestamp added. The user could then commit the amended source files to git.