Consider inertia of the puntual mass.
Add two new subparameters to disable linear or torsion springs.
If spring (linear or torsion) is rigid do not integrate, return the equilibrium position.
Remove unused variable.
New bool subtaparmeter 'Origin drags tip'
Correct mistake from previous commit
Merge pull request #107 from genete/dynamics-2

Dynamics improvements
Require boost >= 1.53.0 at configure time
Fix Bug report #570  -  Renaming a ValueNode with same name, Error message display blank old name

assign "old_name" before checking "new_name"
Add boost librairy lib & include path to synfig lib & include path.