Fix ticket #10388, an occasional failure of temp_directory_path to deal correctly with the trailing separator. A path member function remove_trailing_separator() was added publicly since this may be useful to users.

src/path.cpp

@@ -254,6 +254,13 @@ namespace filesystem
     return *this;
   }
 
+  path&  path::remove_trailing_separator()
+  {
+    if (!m_pathname.empty() && is_separator(m_pathname[m_pathname.size() - 1]))
+      m_pathname.erase(m_pathname.size() - 1);
+    return *this;
+  }
+
   path& path::replace_extension(const path& new_extension)
   {
     // erase existing extension, including the dot, if any