This patch introduces the slider constraint, adds an slider constraint
test, move p2p constraint from ephysics_constraint_add to
ephysics_constraint_p2p_add migrates its usage.
Further work will migrate the btConstraint of p2p for Generic6Dof constraint
since it's flexible enough to implement most of constraints.
Patch by: Leandro Dorileo <dorileo@profusion.mobi>
SVN revision: 74699