Reorganised the Group::removeChild and Geode::removeDrawable methods so

that removeChild(Node*), removeChild(uint) and equivilant Geode methods are
now inline methods, not designed to be overriden, and seperated out the
multiple remove method to be called removeChildren(uint, uint) which is
now the only virtual method.  There removeChildren is now the method to
override in subclasses.

This reorganisation requires some call code to be rename removeChild usage
to removeChildren.

src/osgParticle/ParticleEffect.cpp

@@ -150,7 +150,7 @@ void ParticleEffect::buildEffect()
 
 
     // clear the children.
-    removeChild(0,getNumChildren());
+    removeChildren(0,getNumChildren());
     
     // add the emitter
     addChild(emitter.get());