Build full A matrix and b vector for a MLCP solver interface, to explore Lemke, Dantzig, Newton and other MLCP solvers. The A matrix contains sparsity information.
Added a PGS solver that uses the sparsity of the A matrix, just for testing (the equivalent sequential impulse solver is much faster, not having to allocate the big matrices)

git-svn-id: http://bullet.googlecode.com/svn/trunk@2687 08e121b0-ae19-0410-a57b-3be3395fd4fd