Add support for SWIG2_CSHARP macro to create SWIG 2 backwards compatability mode.

Examples/test-suite/csharp/Makefile.in

@@ -14,6 +14,7 @@ top_builddir = ../@top_builddir@
 
 CPP_TEST_CASES = \
 	csharp_attributes \
+	csharp_swig2_compatability \
 	csharp_exceptions \
 	csharp_features \
 	csharp_lib_arrays \
@@ -36,6 +37,7 @@ CSHARPFLAGSSPECIAL =
 # Custom tests - tests with additional commandline options
 intermediary_classname.cpptest: SWIGOPT += -dllimport intermediary_classname
 csharp_lib_arrays.cpptest: CSHARPFLAGSSPECIAL = -unsafe
+csharp_swig2_compatability.cpptest: SWIGOPT += -DSWIG2_CSHARP
 
 # Rules for the different types of tests
 %.cpptest: 

Examples/test-suite/csharp_swig2_compatability.i

@@ -0,0 +1,48 @@
+%module csharp_swig2_compatability
+
+%typemap(cscode) Foo %{
+
+// Without the using directives generated by the
+// SWIG 2 compatability mode, this code would fail
+// to build.
+public void FooBar(string input)
+{
+  Console.WriteLine(input);
+}
+
+%}
+
+%pragma(csharp) imclasscode=%{
+
+// Without the using directives generated by the
+// SWIG 2 compatability mode, this code would fail
+// to build.
+public void IntermediateClassMethod(string input)
+{
+  Console.WriteLine(input);
+}
+
+%}
+
+%pragma(csharp) modulecode=%{
+
+// Without the using directives generated by the
+// SWIG 2 compatability mode, this code would fail
+// to build.
+public void ModuleClassMethod(string input)
+{
+  Console.WriteLine(input);
+}
+
+%}
+
+%inline %{
+class Foo {
+public:
+  Foo() {}
+  
+  void Bar() {}
+};
+
+%}
+

Lib/csharp/csharp.swg

@@ -11,6 +11,24 @@
  * The imtype typemap contains the C# type used in the intermediary class. 
  * The cstype typemap contains the C# type used in the C# proxy classes, type wrapper classes and module class. */
 
+/* SWIG 3 no longer inserts using directives into generated C# code. For backwards compatability, the SWIG2_CSHARP
+   macro can be defined to have SWIG 3 generate using directives similar to those generated by SWIG 2. */
+#ifdef SWIG2_CSHARP
+
+%typemap(csimports)                   SWIGTYPE, SWIGTYPE *, SWIGTYPE &, SWIGTYPE &&, SWIGTYPE [], SWIGTYPE (CLASS::*) "\nusing global::System;\nusing global::System.Runtime.InteropServices;\n"
+
+%pragma(csharp) moduleimports=%{
+using global::System;
+using global::System.Runtime.InteropServices;
+%}
+
+%pragma(csharp) imclassimports=%{
+using global::System;
+using global::System.Runtime.InteropServices;
+%}
+
+#endif
+
 
 /* Fragments */
 %fragment("SWIG_PackData", "header") {