make-simple-server opens sockets

[Takashi Kato]

It is inconvenient that make-simple-server opens sockets after it's created.

Example:

(import (net server) (sagittarius socket))

(define server (make-simple-server "12345" (lambda (s sock) #t)))

(make-server-socket "12345")

This prevents defining toplevel server on the script which can be used to stop the server.

[Takashi Kato]

Merge with issue-135 (Fixes #135)

→ <<cset e15efb6953bf>>