win32: emulate SIGPIPE

The code to check whether a write error is due to a broken pipe
can now either:

- return with error EPIPE;
- cause the process to exit with code 128+SIGPIPE.

The default is the latter but the behaviour can be changed by issuing
signal(SIGPIPE, SIG_IGN) and signal(SIGPIPE, SIG_DFL) calls.

No actual signal is involved so kill can't send SIGPIPE and handlers
other than SIG_IGN and SIG_DFL aren't supported.

This does, however, avoid unsightly 'broken pipe' errors from commands
like the example in GitHub issue #99:

  dd if=/dev/urandom | tr -dc _A-Z-a-z-0-9 | head -c${1:-32};echo;

0 files changed, 0 insertions, 0 deletions