MatrixBase:

* support resize() to same size (nop). The case of FFT was another case where that make one's life far easier.
   hope that's ok with you Gael. but indeed, i don't use it in the ReturnByValue stuff.

FFT:
 * Support MatrixBase (well, in the case with direct memory access such as Map)
 * adapt unit test

Eigen/src/Core/util/StaticAssert.h

@@ -78,7 +78,8 @@
         INVALID_MATRIX_TEMPLATE_PARAMETERS,
         BOTH_MATRICES_MUST_HAVE_THE_SAME_STORAGE_ORDER,
         THIS_METHOD_IS_ONLY_FOR_DIAGONAL_MATRIX,
-        THE_MATRIX_OR_EXPRESSION_THAT_YOU_PASSED_DOES_NOT_HAVE_THE_EXPECTED_TYPE
+        THE_MATRIX_OR_EXPRESSION_THAT_YOU_PASSED_DOES_NOT_HAVE_THE_EXPECTED_TYPE,
+        THIS_METHOD_IS_ONLY_FOR_EXPRESSIONS_WITH_DIRECT_MEMORY_ACCESS_SUCH_AS_MAP_OR_PLAIN_MATRICES
       };
     };