use c++11 thread_local specifier (remove boost::thread_specific_ptr)

Author: artemp

src/mapnik_python.cpp

@@ -190,7 +190,7 @@ using mapnik::python_unblock_auto_block;
 #ifdef MAPNIK_DEBUG
 bool python_thread::thread_support = true;
 #endif
-boost::thread_specific_ptr<PyThreadState> python_thread::state;
+thread_local std::unique_ptr<PyThreadState> python_thread::state;
 
 struct agg_renderer_visitor_1
 {

src/mapnik_threads.hpp

@@ -22,7 +22,7 @@
 #ifndef MAPNIK_THREADS_HPP
 #define MAPNIK_THREADS_HPP
 
-#include <boost/thread/tss.hpp>         // for thread_specific_ptr
+#include <thread>
 #include <Python.h>
 
 namespace mapnik {
@@ -70,7 +70,7 @@ class python_thread
     }
 
 private:
-    static boost::thread_specific_ptr<PyThreadState> state;
+    static thread_local std::unique_ptr<PyThreadState> state;
 #ifdef MAPNIK_DEBUG
     static bool thread_support;
 #endif