Add support for the -external-runtime argument and update all language modules to use it

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@6993 626c5289-ae23-0410-ae9c-e8d60b6d4f22

SWIG/Source/Modules/python.cxx

@@ -2470,6 +2470,20 @@ public:
     }
     return SWIG_OK;
   }
+
+  virtual String *runtimeCode() {
+    String *s = Swig_include_sys("pyrun.swg");
+    if (!s) {
+      Printf(stderr, "*** Unable to open 'pyrun.swg'\n");
+      s = NewString("");
+    }
+    return s;
+  }
+
+  virtual String *defaultExternalRuntimeFilename() {
+    return NewString("swigpyrun.h");
+  }
+
 };
 
 /* ---------------------------------------------------------------