fix regression from #2250

With #2250 I have unknowingly broken a chain of `invalidateSize(); fitBounds()` calls when map is not loaded, but the container was resized in meantime. It is a complex use-case, involving `getSize()` calls when map is not yet loaded, and using `fitBounds()` for initialization, instead of `setView()`. See [this jsfiddle](http://jsfiddle.net/uA7Pe/1/) (by uncommenting ).

This PR removes `map._sizeChanged` property, since it is basically a parameter to `getSize()` method, and adds `refresh` parameter to `setSize()`. Methods that can call `setView()` (including `fitBounds()`) now call `getSize(true)`, so they always use current values for container size.

I hope this can be merged in *stable* for 0.7.2 release.