[PATCH 0/2] friendlier handling of overflows in archive-tar

The ustar format has some fixed-length numeric fields, and it's possible
to generate a git tree that can't be represented (namely file size and
mtime). Since f2f0267 (archive-tar: use xsnprintf for trivial
formatting, 2015-09-24), we detect and die() in these cases. But we can
actually do the friendly (and POSIX-approved) thing, and add extended
pax headers to represent the correct values.

  [1/2]: archive-tar: write extended headers for file sizes >= 8GB
  [2/2]: archive-tar: write extended headers for far-future mtime

-Peff