Fix inputhook_wx on osx

[lessandro]

Use the inputhook_wx2 implementation on osx, fixing #2762.

Please review. Perhaps it would be better to test with 'cocoa' in wx.version(), write a new implementation without the Pending/Dispatch loop, or just use inputhook_wx2 on all platforms.

[takluyver]

To save other people a moment, we have inputhook_wx{1,2,3}, and their docstrings say:

1. Run the wx event loop by processing pending events only.

   This approach seems to work, but its performance is not great as it
   relies on having PyOS_InputHook called regularly.

2. Run the wx event loop, polling for stdin.

   This version runs the wx eventloop for an undetermined amount of time,
   during which it periodically checks to see if anything is ready on
   stdin. If anything is ready on stdin, the event loop exits.

3. Run the wx event loop by processing pending events only.

   This is like inputhook_wx1, but it keeps processing pending events
   until stdin is ready. After processing all pending events, a call to
   time.sleep is inserted. This is needed, otherwise, CPU usage is at 100%.
   This sleep time should be tuned though for best performance.

At present, we use inputhook_wx3 on all platforms.

[minrk]

I vote for merging this as-is, since the situation is just unusable now. We can look into a better fix if people continue to report trouble with wx.

[ellisonbg]

I agree with @minrk that this should be merged as is. @takluyver do you agree?

[takluyver]

I'm not on OS X, so I can't test it. ;-) But if inputhook_wx3 is unusable there, and inputhook_wx2 at least vaguely works, this seems like a no-brainer.

[ellisonbg]

OK I am going to merge.