Modify prototype of method Problem::applyConstraint

  - return true/false for success/failure,
  - return residual error.
Add an interface method in problem to create a position constraint.
Merge branch 'master' of https://github.com/florent-lamiraux/hpp-corbaserver

Conflicts:
	idl/hpp/corbaserver/problem.idl
	src/problem.impl.cc
	src/problem.impl.hh
error correction for Problem::createPositionConstraint in problem.impl.cc