Explicit casts added

XCode/LLVM project fails to compile without those - there seems to be
some aggressive standards-conforming code generation requirement.
drag scroll changes

make non-inverted drag scrolling grab the map
make inverted drag scroll grab the camera and hide the selection cursor
make it all scale according to display settings
apply the same behaviour to the minimap
Merge pull request #840 from luciderous/master

Explicit casts added
fix tiles at bottom corners
fix fps limiting

don't sdl_delay, skip drawing instead to preserve game/timer speeds
regardless of FPS limit
small adjustment to previous commit

calculate the time until next update as the last operation before
 checking if it's time to update  or not
make the FPS counter as accurate as can be
match FPS up to in-game setting as closely as possible. (the -1)