usage message for newer-mtime in tar 1.13

[Mark Moraes]

1. It says:

  -N, --newer=DATE             only store files newer than DATE
      --newer-mtime            compare date and time when data changed only
      --after-date=DATE        same as -N

Judging by the code, it seems that --newer and --newer-mtime both
take an argument, so shouldn't that be --newer-mtime=DATE

  -N, --newer=DATE             only store files newer than DATE
      --after-date=DATE        same as -N
      --newer-mtime=DATE       same as -N, but compare date and time
                               when only data changed (mtime rather than ctime)


2. Should -N and its usage message really be conditional on !MSDOS?
All MSDOS that I'm familiar with have an mtime in their stat()
structures.

    Mark.