Duplicate parameter name handling improvements

When a method with duplicate parameter names is wrapped such as:

  void fn_3parms(int p_a, int p_a, double p_c);

Previously all duplicate parameter names were changed in order to
provide unique parameter names:
  void fn_3parms(int arg0, int arg1, double p_c)
Now the parameter names changed are just the 2nd and subsequent duplicate
parameter names:
  void fn_3parms(int p_a, int arg1, double p_c)

Examples/test-suite/common.mk

@@ -225,6 +225,7 @@ CPP_TEST_CASES += \
 	director_wombat \
 	disown \
 	duplicate_class_name_in_ns \
+	duplicate_parm_names \
 	dynamic_cast \
 	empty \
 	enum_ignore \

Examples/test-suite/duplicate_parm_names.i

@@ -0,0 +1,21 @@
+%module duplicate_parm_names
+
+// Testing duplicate argument name handling
+
+%{
+void fn_2parms(int, int) {}
+void fn_3parms(int, int, double) {}
+void fn_4parms(int, short, double, const char *) {}
+
+struct SameParmNameCheck {
+  void metho(int, short, double, const char *) {}
+};
+%}
+
+void fn_2parms(int argx, int argx) {}
+void fn_3parms(int p_a, int p_a, double p_c) {}
+void fn_4parms(int duplicate, short duplicate, double duplicate, const char *duplicate) {}
+
+struct SameParmNameCheck {
+  void metho(int dup, short dup, double uniq, const char *dup) {}
+};

Source/Modules/lang.cxx

@@ -3633,15 +3633,20 @@ String *Language::makeParameterName(Node *n, Parm *p, int arg_num, bool setter)
 
   // Check if parameter name is a duplicate.
   int count = 0;
+  Parm *first_duplicate_parm = 0;
   ParmList *plist = Getattr(n, "parms");
   while (plist) {
-    if ((Cmp(pn, Getattr(plist, "name")) == 0))
+    if ((Cmp(pn, Getattr(plist, "name")) == 0)) {
+      if (!first_duplicate_parm)
+	first_duplicate_parm = plist;
       count++;
+    }
     plist = nextSibling(plist);
   }
 
   // If the parameter has no name at all or has a non-unique name, replace it with "argN".
-  if (!pn || count > 1) {
+  // On the assumption that p is pointer/element in plist, only replace the 2nd and subsequent duplicates
+  if (!pn || (count > 1 && p != first_duplicate_parm)) {
     arg = NewStringf("arg%d", arg_num);
   } else {
     // Otherwise, try to use the original C name, but modify it if necessary to avoid conflicting with the language keywords.