Use Volatile wrapper.

Merge branch 'UpdateNUnitTo3' of https://github.com/RogerBestMsft/StackExchange.Redis into netcore-test

Remove usage of SslStream.IsEncrypted as it is not availalbe on dnxcore.  On Desktop it simply returns IsAuthenticated.

Handle "inf" as well as "+inf"

Redis (v2.8 and v3) returns "inf" for positive infinity values, but here a "+inf" is expected. So changed the code to work with both: "+inf" as well as "inf".
See Issue #287: https://github.com/StackExchange/StackExchange.Redis/issues/287

Add package for Timer.  Use SpinWait struct to simulate the Thread.Yield.  According to MSDN it will always yield after the initial several spins.  Simple test shows it yields after 11 spins.

Replace StringComparer.InvariantCultrueIgnoreCase with STringComparer.OrdinalIgnoreCase as the former is almost always incorrect for string equality.

Disable logging of ThreadPool stats for netcore since Get{Max,Min,Available}Threads() are not supported.

Replace unsupported Environment.MachineName with Environment.GetEnvironmentVariable("ComputerName") call.

Remove usage of ThreadPriority for netcore.

#248 Exchanging operands in the ternary operators of server selection in TryResend in ServerSelectionStrategy