big reorganization in JacobiSVD:

- R-SVD preconditioning now done with meta selectors to avoid compiling useless code
- SVD options now honored, with options to hint "at least as many rows as cols" etc...
- fix compilation in bad cases (rectangular and fixed-size)
- the check for termination is now done on the fly, no more goto (should have done that earlier!)

Eigen/src/Core/util/Constants.h

@@ -238,6 +238,15 @@ enum {
   OnTheRight = 2
 };
 
+// options for SVD decomposition
+enum {
+  SkipU = 0x1,
+  SkipV = 0x2,
+  AtLeastAsManyRowsAsCols = 0x4,
+  AtLeastAsManyColsAsRows = 0x8,
+  Square = AtLeastAsManyRowsAsCols | AtLeastAsManyColsAsRows
+};
+
 /* the following could as well be written:
  *   enum NoChange_t { NoChange };
  * but it feels dangerous to disambiguate overloaded functions on enum/integer types.