[#401 #481] [Client] mark Request as connected when reusing keepalive (@xwang1498)
[#401 #481] [Client] mark Request as connected when reusing keepalive (@xwang1498)

Previously, a new Request that reused an existing keepalive conn was never marked as connected, so it would incorrectly use `connect-timeout` instead of `idle-timeout` when deciding whether to timeout.

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