FreeJ2ME doesn't pause in situations where it should

[AShiningRay]

This is mostly an issue on libretro right now, but i can see it being a problem in SDL too once its new UI arrives (but this issue won't cover it, as the UI has to be there first).

So the issue here is, whenever libretro has to pause the core to open up its menu, FreeJ2ME still keeps running the game on the background. This shouldn't be the case unless the user sets the libretro frontend to keep the core running when the menu is up.

Using J2ME's own pauseApp method to pause MIDlets isn't a good approach since many jars don't even implement it to a useful capacity. So the next alternative is to introduce a sleep call into the main thread that sleeps for as long as the libretro frontend has its menu up (since the core is a separate process, this shouldn't cause issues), as for SDL, the only implementation that i can think of at the moment is running its UI on a separate thread along with its input polling.