Changed features that may 'break' old scenes

### 2.6.14 Changed features that may 'break' old scenes

Camera:
The way to controll the `orthographic` camera has changed. The 'old trick' to put the `orthographic` statement all the way at the end of the camera statement results in a error now. Read all about how still to use this feature in Orthographic projection.

Filter:
In layered textures, `filter` used to work the same as `transmit`. It has been changed to work as `filter` should. This can change the appearance of "pre 3.5" textures a lot.
Solution: Use the `#version` directive to switch between desired behavior. An other option in old scenes is to replace the `filter` by `transmit`.

Note: The predefined textures, like in woods.inc, have been changed accordingly.

Gradient:
The `gradient` pattern used to reverse / mirror for negative values along the specified orientation vector. This is not the case anymore.
Solution: If only the range -1 to 1 was used of the old `gradient`, for example in a `sky_sphere`, it can be replaced by the `planar` pattern and revert the color_map. A more general solution is to use `function{abs(x)}` as a pattern instead of `gradient x` and similar for `gradient y` and `gradient z`.

Log:
The float function `log` used to be the natural logarithm, as per version 3.5 it is 10-based. For the, e-based, natural logarithm `ln` is added. This change also affects the `julia_fractal`.
Solution: replace `log` by `ln`.

Media:
In POV-Ray 3.1, it was the use of `filter` or `transmit`, in the media container, that determined whether the media would cast a shadow or not. As per version 3.5 a media always casts a shadow.
Solution: if shadows are not wanted, add the `no_shadow` keyword to the media container.

Noise:
New noise functions have been added in POV-Ray 3.5. Noise functions are internaly used in patterns. The default function in 3.5 is not the same as it was in 3.1 and earlier. This may affect the appearence of textures in old scenes.
Solution: put `noise_generator 1` in `global_settings{}`.

Radiosity:
In POV-Ray 3.1 radiosity calculations were based on the `ambient` value of objects. These calculations are now based on the `diffuse` value of objects. Also many other aspects of radiosity have changed.
Solution: Rewrite the scene.

Note: Radiosity is still an experimental feature, for future POV-Ray versions backwards compatibility can not be guaranteed.

Spotlight:
The default values for the spotlight have changed:
`radius`: 30 (old: 70) degrees
`falloff`: 45 (old: 70) degrees
`tightness`: 0 (old: 10)
Also the `tighness` for cilinder lights has changed to 0 (was: 10).