message: EliminationSolver: better describe two constructors in comments.
diff: @@ -208,6 +208,9 @@ public:
  /** @brief Constructor, elimination is by blocks.
  + Each block is eliminated independently; if the blocks are reasonably
  + small this can be reasonably efficient.
  +
  The nonzeros in B are assumed to be in disjoint rows and columns; the
  rows are identified with the constraint_rowstarts array, the secondary
  dofs are assumed to be the first nonzeros in the rows. */
  