From Chris Lightfoot <[email protected]>: add

From Chris Lightfoot <[email protected]>: add
"pcap_dump_fopen()" to open a pcap_t given a FILE *, and add
"pcap_dump_fopen()" to open a pcap_dumper_t given a FILE *.

On Windows, if we're opening the standard input, put it in binary mode.

Check for errors from "sf_write_header()" and return an error if we get
an error.