[GIT SERIES v2] secnet: fuzz test slip decoder, fd handling fixes

[Ian Jackson]

The following series is available for review here:
  http://www.chiark.greenend.org.uk/ucgi/~ian/git/secnet.git/
  git://git.chiark.greenend.org.uk/~ian/secnet.git
in the following rev-list:
  base.fuzz-slip-decoder.2..proposed.fuzz-slip-decoder.2

 23a1ba6  test-example: Provide a fuzzer for the slip decoder
 6ab18f5  slip: Do not malloc the userv activation context etc.
 845e3f4  fds: Introduce pipe_cloexec()
 cab110d  fds: Simplify fd close condition in tun_set_route
 ccf2502  fds: Provide cloexec() and use it in udp.c and tun.c

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