su: add a delay if the password is incorrect

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
build system: for "find", use POSIX not operator (!) instead of -not

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
script: make it work even if fd 0 is closed

Testcase:
script -q -c "echo hey" /dev/null 0>&-

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>