Added a Lemke MLCP solver, extracted from the MBSim project, and re-licensed under the zlib license

with permission of the original author. 
The Lemke implementation is not fully working yet:
1) we need to convert the lo-high LCP problem into a problem without the lo/high
2) we need to sort out the remaining instabilities, and report a failure if the max loopcount is reached etc.
We replaced the fmatvec library with our own LinearMath/btMatrixX.h, and STL std::vector with btAlignedObjectArray

Removed some warnings/potential issues: use fuzzyZero instead of isZero, and some warnings, 
related to this issue 756

src/BulletDynamics/MLCPSolvers/btLemkeAlgorithm.h

@@ -0,0 +1,108 @@
+/* Copyright (C) 2004-2013 MBSim Development Team
+
+Code was converted for the Bullet Continuous Collision Detection and Physics Library
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+//The original version is here
+//https://code.google.com/p/mbsim-env/source/browse/trunk/kernel/mbsim/numerics/linear_complementarity_problem/lemke_algorithm.cc
+//This file is re-distributed under the ZLib license, with permission of the original author
+//Math library was replaced from fmatvec to a the file src/LinearMath/btMatrixX.h
+//STL/std::vector replaced by btAlignedObjectArray
+
+
+
+#ifndef NUMERICS_LEMKE_ALGORITHM_H_
+#define NUMERICS_LEMKE_ALGORITHM_H_
+
+#include "LinearMath/btMatrixX.h"
+
+
+#include <vector> //todo: replace by btAlignedObjectArray
+
+class btLemkeAlgorithm
+{
+public:
+ 
+
+  btLemkeAlgorithm(const btMatrixXu& M_, const btVectorXu& q_, const int & DEBUGLEVEL_ = 0) :
+	  DEBUGLEVEL(DEBUGLEVEL_)
+  {
+	setSystem(M_, q_);
+  }
+
+  /* GETTER / SETTER */
+  /**
+   * \brief return info of solution process
+   */
+  int getInfo() {
+	return info;
+  }
+
+  /**
+   * \brief get the number of steps until the solution was found
+   */
+  int getSteps(void) {
+	return steps;
+  }
+
+
+
+  /**
+   * \brief set system with Matrix M and vector q
+   */
+  void setSystem(const btMatrixXu & M_, const btVectorXu & q_)
+	{
+		m_M = M_;
+		m_q = q_;
+  }
+  /***************************************************/
+
+  /**
+   * \brief solve algorithm adapted from : Fast Implementation of Lemke’s Algorithm for Rigid Body Contact Simulation (John E. Lloyd)
+   */
+  btVectorXu solve(unsigned int maxloops = 0);
+
+  virtual ~btLemkeAlgorithm() {
+  }
+
+protected:
+  int findLexicographicMinimum(const btMatrixXu &A, const int & pivotColIndex);
+  bool LexicographicPositive(const btVectorXu & v);
+  void GaussJordanEliminationStep(btMatrixXu &A, int pivotRowIndex, int pivotColumnIndex, const btAlignedObjectArray<int>& basis);
+  bool greaterZero(const btVectorXu & vector);
+  bool validBasis(const btAlignedObjectArray<int>& basis);
+
+  btMatrixXu m_M;
+  btVectorXu m_q;
+
+  /**
+   * \brief number of steps until the Lemke algorithm found a solution
+   */
+  unsigned int steps;
+
+  /**
+   * \brief define level of debug output
+   */
+  int DEBUGLEVEL;
+
+  /**
+   * \brief did the algorithm find a solution
+   *
+   * -1 : not successful
+   *  0 : successful
+   */
+  int info;
+};
+
+
+#endif /* NUMERICS_LEMKE_ALGORITHM_H_ */