Make deluxe assertion with deluxe error message with link to deluxe web page

for this very nasty bug (unaligned member in dynamically allocated struct)
that our friends at Krita just encountered:

http://bugs.kde.org/show_bug.cgi?id=177133

CCBUG:177133

Eigen/src/Core/util/Memory.h

@@ -37,6 +37,17 @@ extern "C" int posix_memalign (void **, size_t, size_t) throw ();
 template <typename T, int Size, bool Align> struct ei_aligned_array
 {
   EIGEN_ALIGN_128 T array[Size];
+
+  ei_aligned_array()
+  {
+    ei_assert(reinterpret_cast<unsigned int>(array)%16 == 0
+              && "An array that should have been aligned was allocated at a non-aligned location! "
+                 "Basically, if a struct Foo has a member that's a fixed-size vectorizable Eigen object (like "
+                 "a Eigen::Vector2d) and you dynamically allocate objects of struct Foo, then you need to "
+                 "let struct Foo have an aligned operator new, which you can do like this: "
+                 "struct Foo : Eigen::WithAlignedOperatorNew {... "
+                 "See this page for details: http://eigen.tuxfamily.org/api/UnalignedArrayAssert.html");
+  }
 };
 
 template <typename T, int Size> struct ei_aligned_array<T,Size,false>