Remove Python -safecstrings option.

This option, if used, has not had any effect on Python 3 code since commit a863d3 9 years ago.
I think we can assume that it is not needed for Python 3.
Running the examples and test-suite (Python 2) doesn't change the code
paths with and without -safecstrings because only SWIG_OLDOBJ and SWIG_NEWOBJ
are used in the typemaps and the following code is thus unaltered by -safecstrings
(which sets SWIG_PYTHON_SAFE_CSTRINGS):

%#if defined(SWIG_PYTHON_SAFE_CSTRINGS)
  if (*alloc != SWIG_OLDOBJ)
%#else
  if (*alloc == SWIG_NEWOBJ)
%#endif
  {
    *cptr = %new_copy_array(cstr, len + 1, char);
    *alloc = SWIG_NEWOBJ;
printf("safe strings: %s\n", *cptr ? *cptr : "NULLSTRING");
  } else {
    *cptr = cstr;
    *alloc = SWIG_OLDOBJ;
  }

Note: nosafecstrings was also the default and -O didn't actually change this.

Lib/python/pystrings.swg

@@ -38,21 +38,7 @@ SWIG_AsCharPtrAndSize(PyObject *obj, char** cptr, size_t* psize, int *alloc)
 %#endif
     if (cptr) {
       if (alloc) {
-	/* 
-	   In python the user should not be able to modify the inner
-	   string representation. To warranty that, if you define
-	   SWIG_PYTHON_SAFE_CSTRINGS, a new/copy of the python string
-	   buffer is always returned.
-
-	   The default behavior is just to return the pointer value,
-	   so, be careful.
-	*/ 
-%#if defined(SWIG_PYTHON_SAFE_CSTRINGS)
-	if (*alloc != SWIG_OLDOBJ) 
-%#else
-	if (*alloc == SWIG_NEWOBJ) 
-%#endif
-	{
+	if (*alloc == SWIG_NEWOBJ) {
 	  *cptr = %new_copy_array(cstr, len + 1, char);
 	  *alloc = SWIG_NEWOBJ;
 	} else {

Source/Modules/python.cxx

@@ -84,7 +84,6 @@ static int nothreads = 0;
 static int classptr = 0;
 /* Other options */
 static int shadowimport = 1;
-static int safecstrings = 0;
 static int dirvtable = 0;
 static int doxygen = 0;
 static int fastunpack = 0;
@@ -144,18 +143,15 @@ static const char *usage3 = "\
      -noproxy        - Don't generate proxy classes \n\
      -noproxyimport  - Don't insert proxy import statements derived from the %import directive \n\
      -nortti         - Disable the use of the native C++ RTTI with directors\n\
-     -nosafecstrings - Avoid extra strings copies when possible (default)\n\
      -nothreads      - Disable thread support for the entire interface\n\
      -olddefs        - Keep the old method definitions even when using fastproxy\n\
      -oldrepr        - Use shorter and old version of __repr__ in proxy classes\n\
      -outputtuple    - Use a PyTuple for outputs instead of a PyList (use carefully with legacy interfaces) \n\
      -py3            - Generate code with Python 3 specific features and syntax\n\
      -relativeimport - Use relative python imports \n\
-     -safecstrings   - Use safer (but slower) C string mapping, generating copies from Python -> C/C++\n\
      -threads        - Add thread support for all the interface\n\
      -O              - Enable the following optimization options: \n\
-                         -fastdispatch -nosafecstrings -fvirtual\n\
-                         -fastproxy -fastunpack\n\
+                         -fastdispatch -fastproxy -fastunpack -fvirtual\n\
 \n";
 
 static String *getSlot(Node *n = NULL, const char *key = NULL, String *default_slot = NULL) {
@@ -393,12 +389,6 @@ public:
 	  /* Turn off thread support mode */
 	  nothreads = 1;
 	  Swig_mark_arg(i);
-	} else if (strcmp(argv[i], "-safecstrings") == 0) {
-	  safecstrings = 1;
-	  Swig_mark_arg(i);
-	} else if (strcmp(argv[i], "-nosafecstrings") == 0) {
-	  safecstrings = 0;
-	  Swig_mark_arg(i);
 	} else if (strcmp(argv[i], "-dirvtable") == 0) {
 	  dirvtable = 1;
 	  Swig_mark_arg(i);
@@ -459,7 +449,6 @@ public:
 	  no_header_file = 1;
 	  Swig_mark_arg(i);
 	} else if (strcmp(argv[i], "-O") == 0) {
-	  safecstrings = 0;
 	  classptr = 0;
 	  fastunpack = 1;
 	  fastproxy = 1;
@@ -485,7 +474,8 @@ public:
 		   strcmp(argv[i], "-fastquery") == 0 ||
 		   strcmp(argv[i], "-modern") == 0 ||
 		   strcmp(argv[i], "-modernargs") == 0 ||
-		   strcmp(argv[i], "-noproxydel") == 0) {
+		   strcmp(argv[i], "-noproxydel") == 0 ||
+		   strcmp(argv[i], "-safecstrings") == 0) {
 	  Printf(stderr, "Deprecated command line option: %s. This option is now always on.\n", argv[i]);
 	} else if (strcmp(argv[i], "-buildnone") == 0 ||
 		   strcmp(argv[i], "-classic") == 0 ||
@@ -494,6 +484,7 @@ public:
 		   strcmp(argv[i], "-nobuildnone") == 0 ||
 		   strcmp(argv[i], "-nomodern") == 0 ||
 		   strcmp(argv[i], "-nomodernargs") == 0 ||
+		   strcmp(argv[i], "-nosafecstrings") == 0 ||
 		   strcmp(argv[i], "-proxydel") == 0) {
 	  Printf(stderr, "Deprecated command line option: %s. This option is no longer supported.\n", argv[i]);
 	  SWIG_exit(EXIT_FAILURE);
@@ -645,10 +636,6 @@ public:
       Printf(f_runtime, "#define SWIG_PYTHON_THREADS\n");
     }
 
-    if (safecstrings) {
-      Printf(f_runtime, "#define SWIG_PYTHON_SAFE_CSTRINGS\n");
-    }
-
     if (!dirvtable) {
       Printf(f_runtime, "#define SWIG_PYTHON_DIRECTOR_NO_VTABLE\n");
     }