Add <string> fragment

Removes <string> include specifically for clang
Cuts down on duplicate #include <string> in general

Lib/tcl/std_vector.i

@@ -28,11 +28,11 @@
 //      is returned
 // ------------------------------------------------------------------------
 
+%fragment("<string>");
 %{
 #include <vector>
 #include <algorithm>
 #include <stdexcept>
-#include <string>
 
 Tcl_Obj* SwigString_FromString(const std::string &s) {
     return Tcl_NewStringObj(s.data(), (int)s.length());