Interface specification for .target.passwd.

1. What is the .target.passwd

.target.passwd can be used to set or modify the encrypted password of
*already existing* users in /etc/passwd and /etc/shadow.

2. Interface for .target.passwd

The path prefix used is

 .target.passwd

Only the Write() interface is supported.

To modify e.g. the password field of user root, the following SCR call
must be used

 SCR(`Write(.target.passwd.root, crypt(a_passwd) ))

This Function returns true on success and false, if it fails.
