Added initial NEON support, most tests pass however we had to use some hackish workarounds

as gcc on ARM (both CodeSourcery 4.4.1 used and experimental 4.5) fail to
ensure proper alignment with __attribute__((aligned(16))). This has to be
fixed upstream to remove the workarounds.

Eigen/src/Core/util/Memory.h

@@ -424,7 +424,7 @@ inline static Integer ei_first_aligned(const Scalar* array, Integer size)
   * ei_aligned_stack_free(data,float,array.size());
   * \endcode
   */
-#ifdef __linux__
+#if (defined __linux__) && !(defined __ARM_NEON__)
   #define ei_aligned_stack_alloc(SIZE) (SIZE<=EIGEN_STACK_ALLOCATION_LIMIT) \
                                     ? alloca(SIZE) \
                                     : ei_aligned_malloc(SIZE)