Initialize the HadContextSensitiveCondition

So there's some reasonable chance of using the optimization.
Avoid invoking IsOff and ConvertToUnixPaths for cached includes

They seem to contribute a surprising amount to the cost of the
function.
Merge topic 'tll-includes-defines' into next

c6289d9 Avoid invoking IsOff and ConvertToUnixPaths for cached includes
4085273 Initialize the HadContextSensitiveCondition