Support for capturing packet data from a pipe (a FIFO, or standard input).

Support for capturing packet data from a pipe (a FIFO, or standard input).

capture.c :
- modified capture() to try to open an interface as a pipe if pcap_open_live()
  failed, and then read data in libpcap format from this pipe ;
- add new functions used by capture() : pipe_open_live() and pipe_dispatch()
  which are equivalents to the pcap_ functions.

libpcap.[ch] :
- moved the MAGIC and headers definitions from libpcap.c to libpcap.h
  because capture() now needs it.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2181 f5534014-38df-0310-8fa8-9805f1628bb7