Changed error message that just said "open %s: %s" to "cannot create %s: %s"

in receiver.c because it confuses people when they do something like
    rsync /etc/passwd /tmp/nonexistentdir/passwd
and it printed out something like
    open /tmp/noniexistentdir/.passwd.a004d5 : No such file or directory
Reported by kurt_granroth@pobox.com in PR #1253.