Patch: 'ldapmodify -y file' reads password from file (ITS#2031)

            ================
Written by Hallvard B. Furuseth and placed into the public domain.
This software is not subject to any license of the University of Oslo.
            ================
Adapted by Kurt Zeilenga for inclusion in OpenLDAP.  My comments are
marked with enclosed with square brackets (e.g. [Kurt's comment] below.
            ================

If I run ldapmodify & co from a script, I don't want to use '-W password'
because the password shows up in the output of 'ps' for everyone,
and I can't pipe the password to 'ldapmodify -w' because -w uses
getpassphrase() which reads from the tty instead of stdin.
So I added '-y file' which reads the password from file.  The programs
exit if the file cannot be read.

[Complete contents of file is used as password.  Use:
	echo -n "secret" > password
to create a file with "secret" as the password.  The -n avoids
adding a newline (which would invalidate the password).  Note
that echo is a builtin and hence its arguments are not visible
to 'ps'.]

I changed ldapmodify, ldapmodrdn, ldapdelete, ldapsearch, ldapcompare.
I did not bother to change ldappasswd and ldapwhoami, because they
prompt for many passwords.  [I fixed up ldapwhoami.]

Rerun autoconf after applying this patch. [Done.]

Note:  I do not know if Windows NT has fstat(), so I set HAVE_FSTAT to
undef in portable.nt.  (fstat() is used to warn if the file is publicly
readable or writeable.)  [I used fstat() to set the buffer size to
read.]

[Note: using the contents of a file extends the tools to support
passwords which could not normally be provided using getpassphrase()
or via the command line.]

Hallvard B. Furuseth <h.b.furuseth@usit.uio.no>, Aug 2002.
[Kurt D. Zeilenga <kurt@openldap.org>, Aug 2002.]