HTTP likes to slap an infinite read deadline on a connection and
do a blocking read while the response is being written.
This effectively means that a reading deadline becomes the
request-response deadline.
Instead of enforcing our timeout, we pass it through and keep
"infinite deadline" is sticky on connections.
However, we still "record" when reads are aborted, so we never overwrite that.
The HTTP server should have `ReadTimeout` and `IdleTimeout` set for the deadline to be effective.
Use --idle-timeout for incoming connections.
Since DeadlineConn would send deadline updates directly upstream,
it would race with Read/Write operations. The stdlib will perform a read,
but do an async SetReadDeadLine(unix(1)) to cancel the Read in
`abortPendingRead`. In this case, the Read may override the
deadline intended to cancel the read.
Stop updating deadlines if a deadline in the past is seen and when Close is called.
A mutex now protects all upstream deadline calls to avoid races.
This should fix the short-term buildup of...
```
365 @ 0x44112e 0x4756b9 0x475699 0x483525 0x732286 0x737407 0x73816b 0x479601
# 0x475698 sync.runtime_notifyListWait+0x138 runtime/sema.go:569
# 0x483524 sync.(*Cond).Wait+0x84 sync/cond.go:70
# 0x732285 net/http.(*connReader).abortPendingRead+0xa5 net/http/server.go:729
# 0x737406 net/http.(*response).finishRequest+0x86 net/http/server.go:1676
# 0x73816a net/http.(*conn).serve+0x62a net/http/server.go:2050
```
AFAICT Only affects internode calls that create a connection (non-grid).
