Fix detection of collisions with the center point. Fix #397.

This fixes separators.

The center point was flat instead of having a size of 1x1.
This bug appeared in commit 9beb1a17, where flat rectangles are no longer
considered overlapping.
Give a size of 1x1 to the ground point.
Fix crash at exit with a moving surface. Fix #398.
Set surfaces in software destination mode by default. Fix #395.

Hardware surfaces are intented to internal optimizations, support
less operations and have a slightly different behavior.
Software surfaces are the most general ones, and also often the best
choice for performance.
Only center window when its size changes or returning from fullscreen.
Quick fix for infinite recursion when switching modes with a draw cycle.

When switching from an accelerated to a software video mode, the code to
build a software surface from a hardware one is buggy and will need a
better fix.
Fix comment.
Fix crash when starting a game during a transition. Fix #399.
Don't try to catch up one-time huge lags. Fix #374.

Falsify the measured time instead.

This prevents the game from running very fast for a few seconds to catch
up after a slow operation was done, like loading a big file, or after
the process was unsuspended.
Merge branch 'master' into grid_draw

Conflicts:
	src/entities/NonAnimatedRegions.cpp
Correctly show animated tiles overlapping non-animated ones.