alpha 3.1. in this commit:

- finally get the Eval stuff right. get back to having Eval as
  a subclass of Matrix with limited functionality, and then,
  add a typedef MatrixType to get the actual matrix type.
- add swap(), findBiggestCoeff()
- bugfix by Ramon in Transpose
- new demo: doc/echelon.cpp

doc/snippets/Eval_MatrixType.cpp

@@ -0,0 +1,13 @@
+typedef Matrix3i MyMatrixType;
+MyMatrixType m = MyMatrixType::random(3, 3);
+cout << "Here's the matrix m:" << endl << m << endl;
+typedef Eigen::Eval<Eigen::Row<MyMatrixType> >::MatrixType MyRowType;
+// now MyRowType is just the same typedef as RowVector3i
+MyRowType r = m.row(0);
+cout << "Here's r:" << endl << r << endl;
+typedef Eigen::Eval<Eigen::Block<MyMatrixType> >::MatrixType MyBlockType;
+MyBlockType c = m.corner(Eigen::TopRight, 2, 2);
+// now MyBlockType is a a matrix type where the number of rows and columns
+// are dynamic, but know at compile-time to be <= 2. Therefore no dynamic memory
+// allocation occurs.
+cout << "Here's c:" << endl << c << endl;