Description:
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On 64-bit systems, keys with non-ascii characters aren't handled correctly. The following code returns false on 32-bit systems, but "value" on 64-bit systems.

It seems like non-ascii characters are simply replaced with _.

Reproduce code:
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$c = new MemCache();
$c->connect("localhost");
$c->flush();

$c->set("?", "value");
var_dump($c->get("?"));

Expected result:
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false

Actual result:
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"value"