Import bmake-20130330
Tag bmake-20130330
Update to bmake-20130330
sh: Write as much into the heredoc pipe as possible, to avoid forking.

Use non-blocking I/O to write as much as the pipe will accept (often 64K,
but it can be as little as 4K), avoiding the need for the ugly PIPESIZE
constant. If PIPESIZE was set too high, a deadlock would occur.