fix the problem with interrupted recv

in perl before 5.14 if recv was interrupted in certain conditions
it sets $! to 0 instead of expected EINTR. The following script
demonstrates the issue, it works on 5.14 but fails if run by perl
5.10:

    use strict;
    use warnings;
    use RedisDB 2.07;

    my $pub = RedisDB->new;
    my $sub = RedisDB->new;
    $sub->subscribe('foo');
    $sub->get_reply;

    local $SIG{ALRM} = sub { $pub->publish( 'foo', 'bar' ); };
    alarm 2;
    $sub->get_reply;

fixes #11

lib/RedisDB.pm

@@ -439,7 +439,7 @@ sub get_reply {
     while ( not @{ $self->{_replies} } ) {
         my $ret = $self->{_socket}->recv( my $buffer, 131072 );
         unless ( defined $ret ) {
-            next if $! == EINTR;
+            next if $! == EINTR or $! == 0;
             confess "Error reading reply from server: $!";
         }
         if ( $buffer ne '' ) {