In a dump_open routine, you don't need to seek to the beginning of the

In a dump_open routine, you don't need to seek to the beginning of the
file before doing any writes - it starts out at the beginning of the
file.  This means that you *can* write a Network Instruments capture
file to a pipe, or write it out in compressed form, now that its
dump_open routine no longer seeks.

NetXRay format and K12 binary format, however, *do* require a seek when
writing them.

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