Merge branch 'rs/archive-mtime'

"git archive HEAD^{tree}" records the paths with the current
timestamp in the archive, making it harder to obtain a stable
output.  The command learned the --mtime option to specify an
arbitrary timestamp (e.g. --mtime="@0 +0000" for the epoch).

* rs/archive-mtime:
  archive: add --mtime

diff --cc archive.c
Simple merge