Line: Side relative accessors; made private more instance data

Line::Side now features a set of side relative accessors enabling
users of the class to implement their algorithms more expressively.

Made use of the new functionality to simplify various algorithms
in the FakeRadio and light decoration modules.

The client-only FakeRadio data for line was moved to that module.

Applied the pimpl idiom to Line::Side and Line::Side::Section and
added a Line::FlagsChange audience (which Line::Side observes on
client side).

Plus significant clean up.

doomsday/client/include/map/bsp/lineinfo.h

@@ -74,7 +74,7 @@ struct LineInfo
            (de::abs(from.origin()[VY] - to.origin()[VY]) < distEpsilon))
             flags |= ZeroLength;
 
-        if(line->hasBackSections() && line->hasFrontSections())
+        if(line->hasFrontSections() && line->hasBackSections())
         {
             flags |= Twosided;
 

doomsday/client/include/map/hedge.h

@@ -124,7 +124,7 @@ class HEdge : public de::MapElement
     /// Accurate length of the segment (v1 -> v2).
     coord_t _length;
 
-    /// For each @ref SideSection.
+    /// For each section of a Line::Side.
     biassurface_t *_bsuf[3];
 
     /// @ref hedgeFrameFlags
@@ -396,7 +396,7 @@ class HEdge : public de::MapElement
     /**
      * Prepare wall division data for a section of the HEdge.
      *
-     * @param section        Section to prepare divisions for.
+     * @param section        Line::Side section to prepare divisions for.
      * @param frontSector    Sector to use for the front side.
      * @param backSector     Sector to use for the back side.
      * @param leftWallDivs   Division data for the left edge is written here.
@@ -406,7 +406,7 @@ class HEdge : public de::MapElement
      * @return  @c true if divisions were prepared (the specified @a section has a
      *          non-zero Z axis height).
      */
-    bool prepareWallDivs(SideSection section, Sector *frontSector, Sector *backSector,
+    bool prepareWallDivs(int section, Sector *frontSector, Sector *backSector,
         walldivs_t *leftWallDivs, walldivs_t *rightWallDivs, pvec2f_t matOffset) const;
 
     /**