-Wpointer-sign: python/.

This fixes -Wpointer-sign warnings in the python/ code in the manner
that seems most appropriate to me.

gdb/
2013-04-19  Pedro Alves  <palves@redhat.com>

	* python/py-inferior.c (infpy_write_memory): Add cast to gdb_byte
	* python/py-prettyprint.c (print_string_repr): Change type of
	'output' local to char *.  Add cast to gdb_byte * in
	LA_PRINT_STRING call.
	(print_children): Change type of 'output' local to char *.
	* python/py-value.c (valpy_string): Add cast to const char * in
	PyUnicode_Decode call.

gdb/python/py-inferior.c

@@ -513,7 +513,7 @@ infpy_write_memory (PyObject *self, PyObject *args, PyObject *kw)
 	  error = 1;
 	  break;
 	}
-      write_memory_with_notification (addr, buffer, length);
+      write_memory_with_notification (addr, (gdb_byte *) buffer, length);
     }
 #ifdef IS_PY3K
   PyBuffer_Release (&pybuf);