bugfix in compute_matrix_flags, optimization in LU,
improve doc, and workaround aliasing detection in MatrixBase_eval snippet
(not very nice but I don't know how to do it in a better way)
diff --git a/doc/snippets/MatrixBase_eval.cpp b/doc/snippets/MatrixBase_eval.cpp
index 7322930..d704245 100644
--- a/doc/snippets/MatrixBase_eval.cpp
+++ b/doc/snippets/MatrixBase_eval.cpp
@@ -4,7 +4,7 @@
cout << "Here is the matrix m:" << endl << m << endl;
cout << "Now we want to replace m by its own transpose." << endl;
cout << "If we do m = m.transpose(), then m becomes:" << endl;
-m = m.transpose();
+m = m.transpose() * 1;
cout << m << endl << "which is wrong!" << endl;
cout << "Now let us instead do m = m.transpose().eval(). Then m becomes" << endl;
m = M;