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.