Move fclose_deleter and null_deleter to their own namespaces to block ADL.

This prevents bringing namespace boost into ADL when the deleters are used
in template parameters, e.g. in std::unique_ptr.

include/boost/core/fclose_deleter.hpp

@@ -26,6 +26,9 @@
 
 namespace boost {
 
+// Block unintended ADL
+namespace fclose_deleter_ns {
+
 //! A function object that closes a file
 struct fclose_deleter
 {
@@ -41,6 +44,10 @@ struct fclose_deleter
     }
 };
 
+} // namespace fclose_deleter_ns
+
+using fclose_deleter_ns::fclose_deleter;
+
 } // namespace boost
 
 #endif // BOOST_CORE_FCLOSE_DELETER_HPP

include/boost/core/null_deleter.hpp

@@ -27,6 +27,9 @@
 
 namespace boost {
 
+// Block unintended ADL
+namespace null_deleter_ns {
+
 //! A function object that does nothing and can be used as an empty deleter for \c shared_ptr
 struct null_deleter
 {
@@ -39,6 +42,10 @@ struct null_deleter
     void operator() (T*) const BOOST_NOEXCEPT {}
 };
 
+} // namespace null_deleter_ns
+
+using null_deleter_ns::null_deleter;
+
 } // namespace boost
 
 #endif // BOOST_CORE_NULL_DELETER_HPP