New option: -B, to force password prompt in batch mode.

With -B, kc will always prompt for a password when -b is also specified
(thus using batch mode), instead of waiting for it on stdin.

(cherry picked from commit 39240cb8ae7f4fb2ccfa811f3b7ace1f0ec53a97)

Conflicts:
	kc.c
Extend Changelog with the -B option.