We had too many spurious test failures in the past.
But on a developer machine, the tests don't usually fail because the
system isn't loaded as much.
So, only disable test on CircleCI.
- `timeoutconn` handles state, yet calls to Read/Write make a copy of
that state (non-pointer receiver) so any outbound calls will not have
the state updated
- Even without the copy issue, the renew methods can in edge cases set a
new deadline _after_ DisableTimeouts have been called, consider the
following racy behavior:
1. `renewReadDeadline` is called, checks `renewDeadlinesDisabled`
(not disabled)
2. `DisableTimeouts` is called, sets `renewDeadlinesDisabled`
3. `DisableTimeouts` invokes `c.SetDeadline`
4. `renewReadDeadline` invokes `c.SetReadDeadline`
To fix the above, the `Conn` receiver was made to be a pointer
everywhere and access to renewDeadlinesDisabled is now guarded
by an RWMutex instead of using atomics.
closes#415
