more strict argument checks for Cache::Memcached->new

[Tokuhiro Matsuno]

I think, Cache::Memcached->new(servers => ['127.0.0.1:11211']) makes
very difficult to detect bug.
Please add the more strict checks.

Index: lib/Cache/Memcached.pm
===================================================================
--- lib/Cache/Memcached.pm      (revision 555)
+++ lib/Cache/Memcached.pm      (working copy)
@@ -11,6 +11,7 @@
 use warnings;

 no strict 'refs';
+use Carp;
 use Storable ();
 use Socket qw( MSG_NOSIGNAL PF_INET PF_UNIX IPPROTO_TCP SOCK_STREAM );
 use IO::Handle ();
@@ -65,6 +66,7 @@
     $self = fields::new( $self ) unless ref $self;

     my ($args) = @_;
+    croak "Cache::Memcached->new required hashref: $args" unless ref
$args eq "HASH";

     $self->set_servers($args->{'servers'});
     $self->{'debug'} = $args->{'debug'} || 0;