React-router v3 compatibility

[unRob]

This "fix" feels like a hack, but it works well to prevent the error Uncaught TypeError: Cannot read property 'key' of null when using this library with react-router v3. All tests that passed without the change still do.

[taion]

That's really not the point. The incompatibility with history v3 is because history v3 has different semantics around the initial location – listen doesn't call the listener immediately with the initial location. It's not about hiding getCurrentLocation, or I wouldn't have added that check to React Router in the first place.

[taion]

Among other things, if you want to do this correctly, you must not invoke the listeners with the initial location in listen.

There's no point in making this library compatible with both history v2 and history v3, either – they're incompatible peer dependencies at any rate.

[taion]

Okay, on closer reading, this is close enough that I'll re-open the PR, but this PR needs to actually follow history v3 semantics before it's mergeable, and it needs to not fail the coverage check as well.

[unRob]

Sorry I haven't found the time to work on this, but I hope this weekend I'll jump back on it. Still a bit confused at what you mean by follow history v3 semantics, could you clarify?

[taion]

listen should not immediately call back with the current location

[taion]

#107 supersedes this by removing the history integration entirely. There's no need to handle any of this just to be compatible with React Router v3, though bugs in history relating to hash history will still prevent scroll management from working correctly in such cases.