Fix freeze when using threaded RTS on windows

[wrvn]

There is a bug on Windows with recent versions of gtk (tested with 2.24.24, 2.24.25 and 3.14.8) that causes whole application to freeze when moving window. Also its mentioned here #33.

The underlying issue is somewhere deep in gtk callback hell where gdk_threads_enter() is getting called twice resulting in deadlock.

The only reason this issue is not observed in non threaded programs is becaue gdk_threads_init() is only called when compiling with -threaded.

This workaround simply replaces default gdk locking functions that use nonrecursive mutex with those that use recursive one.

Also here is simple c program that demonstrates this issue http://pastebin.com/5Gz2KdmA.

[emmanueltouzery]

I mentioned in issue #33 having the problem. I now rebuilt my program for windows.
First I rebuilt it with the gtk3 package without the fix and sure enough, freeze when I attempt the resize the window.
Then I applied the fix. No more freeze! I then did a basic testing of the application, and it does appear to perform correctly the multithreading, that means with correct performance unlike what I was getting when disabling the threaded RTS.

So I'm pretty sure the fix is correct and fixes completely the problem! I'll keep tuning my app for windows now that a port is finally possible and write here if I find something strange but I am certain I won't. Great work, thanks and I hope this gets merged ASAP!

Maybe @cchantep wants to check too, as he was active in the issue #33 and maybe he didn't notice this PR?