Detached process should not have pipe as its current ports.

[Takashi Kato]

When process is detached, the parent process may finish before the detached process (most of the time). In such cases, the pipe set to current ports are closed on parent process and if detached processes output to current port, then the outputs go nowhere.

Proposal to resolve this issue:

1. Make sys-process-call to accept extra keyword argument to specify where current ports are redirected.
2. When :detach is #t, sys-process-call should redirect detached processes current ports to standard input/ouput.

The first one is preferable.

[Takashi Kato]

Done on POSIX.

[Takashi Kato]

Adding Windows implementation of redirect process input/output. Renaming stdin, stdout and stderr keywords. (it's invalid on MSVC) Fixes #177

→ <<cset b18bbcd74da2>>