MacOS: bsdtar doesn't save/restore bkuptime

Split out from Issue 155:  A general test suite used to verify file backup and 
copy utilities on Mac OS has found that bsdtar 2.6.2 does not save/restore 
bkuptime.

See Issue 155 for more details.

The source code for the particular test is here:
   https://github.com/neoneye/AnalyzeCopy/blob/master/Tests/91_bkuptime.rb

The test fails part 'A'.  (The file is copied but the backup time is not 
preserved.)

Archiving bkuptime should be routine:  It's easy to extend archive_entry to 
support a new time, and easy to add another attribute to the pax writer to save 
it.

Restoring bkuptime should also be routine.

The hard part is figuring out when bkuptime should be restored.  I don't think 
backup time should be restored by default.  The restored file is, after all, a 
new file.  The policy in bsdtar has been to tie extra metadata to the -p 
option, though that might be inappropriate as well.

I'm marking this as "Low Priority" since I expect it to only be used behind a 
special option, and therefore expect it to receive very little use.

Original issue reported on code.google.com by kientzle@gmail.com on 22 Jan 2012 at 11:20

pombreda / libarchive

MacOS: bsdtar doesn't save/restore bkuptime #230