nvi - Work around problem with git

nvi - Work around problem with git

* When a vi session managed by a git commit is ^Z'd and then resumed, git
  for some reason will set STDIN to O_NONBLOCKING.  Not only will it do
  this, but the git process will do it in parallel with the resume so
  the point at which stdin becomes non-blocking from the point of view
  of vi is completely non-determinisitc.

* Do an end-run around badly behaving parent processes by using extpread()
  to explicitly override the blocking/non-blocking mode.  Now nvi doesn't
  care whether stdin is in non-blocking mode or not.