Extend C# complex support to member variables of this type

Define csvar{in,out} typemaps needed to support properties of complex type and
apply the existing cstype and csin ones to them as well.

Add unit test verifying that this works as expected in C# and, also, in
Python, even though no changes were needed there.

Examples/test-suite/complextest.i

@@ -34,6 +34,11 @@
     return b;
   }  
 #endif
+
+  struct ComplexPair
+  {
+    std::complex<double> z1, z2;
+  };
 }