bug#21497: install from multiple sources to -t target uses incorrect folder on some sources

[Chris Severance]

The following script of 4 equivalent installs does not complete.

#!/usr/bin/bash

set -e
set -u

# Bug report for install (GNU coreutils) 8.24
# Arch Linux gq 4.1.6-1-ARCH #1 SMP PREEMPT Mon Aug 17 08:52:28 CEST
2015 x86_64 GNU/Linux
# The following 4 install do the same thing. One will fail.

rm -rf 'testin' 'testout'
mkdir -p 'testin/d2'
touch 'testin/f1' 'testin/d2/f2' 'f3'
echo 'Try 1'
install -Dpm644 'testin/f1' 'testin/d2/f2' 'f3' -t "${PWD}/testout/"
rm -rf 'testout'
echo 'Try 2'
install -Dpm644 "${PWD}/testin/f1" "${PWD}/testin/d2/f2" 'f3' -t
"testout/"
rm -rf 'testout'
echo 'Try 3'
install -Dpm644 'f3' "${PWD}/testin/f1" "${PWD}/testin/d2/f2" -t
"${PWD}/testout/"
rm -rf 'testout'
echo 'Try 4 will fail'
install -Dpm644 "${PWD}/testin/f1" "${PWD}/testin/d2/f2" 'f3' -t
"${PWD}/testout/"
# install: cannot stat 'f3': No such file or directory