Revert changes on memcpy matrix getters

Fix issue Qucs#133

The C memcpy was replaced by loops, but it causes the kernel to segfault
during SP analysis with Noise.

memcpy is good with POD and tends to be inlined [1].
Replacement candidate is std:copy. Please provide testcase and
testbench.

[1] http://nadeausoftware.com/articles/2012/05/c_c_tip_how_copy_memory_quickly

qucs-core/src/circuit.cpp

@@ -653,9 +653,7 @@ void circuit::setMatrixS (matrix s) {
    circuit. */
 matrix circuit::getMatrixS (void) {
   matrix res (size);
-  for(unsigned int i=0; i < size; ++i)
-    for(unsigned int j=0; i < size; ++j)
-      res(i,j) = MatrixS[i*size + j];
+  memcpy (res.getData (), MatrixS, sizeof (nr_complex_t) * size * size);
   return res;
 }
 
@@ -674,9 +672,7 @@ void circuit::setMatrixN (matrix n) {
    matrix of the circuit. */
 matrix circuit::getMatrixN (void) {
   matrix res (size);
-  for(unsigned int i=0; i < size; ++i)
-    for(unsigned int j=0; i < size; ++j)
-      res(i,j) = MatrixN[i*size + j];
+  memcpy (res.getData (), MatrixN, sizeof (nr_complex_t) * size * size);
   return res;
 }
 
@@ -695,9 +691,7 @@ void circuit::setMatrixY (matrix y) {
    circuit. */
 matrix circuit::getMatrixY (void) {
   matrix res (size);
-  for(unsigned int i=0; i < size; ++i)
-    for(unsigned int j=0; i < size; ++j)
-      res(i,j) = MatrixY[i*size + j];
+  memcpy (res.getData (), MatrixY, sizeof (nr_complex_t) * size * size);
   return res;
 }