Try to solve even very overconstrained systems.

Before this commit, overconstraining a system past a certain point
resulted in a wrong error message: instead of "redundant constraints",
"unsolvable constraints" was displayed.

To reproduce, place more six or more length constraints with the same
value onto the same line segment.

src/system.cpp

@@ -278,7 +278,6 @@ bool System::SolveLeastSquares(void) {
 }
 
 bool System::NewtonSolve(int tag) {
-    if(mat.m > mat.n) return false;
 
     int iter = 0;
     bool converged = false;