MapCollision: check_line: remove float_round

The arguments passed to is_valid_position may be a float, as it is
implemented as
	bool MapCollision::is_valid_position(
					float x, float y,
					MOVEMENTTYPE movement_type,
					bool is_hero) const
	{
		return is_valid_tile(floor(x), floor(y),
					movement_type, is_hero);
	}

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
MapCollision::is_wall: change signature to accept float

Nearly all the other functions in MapCollision accept float, so this
must have been overlooked. By changing the function to accept float, we
can remove the rounding/flooring from all calling points moving it into
the function itself.

Similar as is_empty(float, float) this also needs to access the the
collision layer, so it needs to transform the floats to integers.
In is_empty we chose floor, which makes sense here as well. This is a
change of semantics (before some places used round instead of floor).

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
MapRenderer: Use floor instead of round for determining upper corner.

I could not find any glitches there, as we have a small safety margin
anyway around the visible screen.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Remove float_round(float), round(FPoint)

We don't use round any more, just floor.
Hopefully we don't need rounding any more, as it introduces some hassle
(it's defined in C++11, but not in previous standards, the windows guys
have a macro(?) instead of a function).

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
MapRenderer: rename local variables

This renames the variable 'upperright' to 'upperleft' as it is the
point on the screen at (0,0), which is at the upper left corner of the
screen.
Just renaming, no function changes.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>