Copied std::pair<> fragment from Lib/std/std_map.i into Lib/std/std_multimap.i. This fixes an error when a std::multimap template is wrapped by itself.
Fix for missing C++ code in std::multimap wrappers.

%template for a std::multimap generated uncompilable code unless a
%template for a std::map of the same template types was also coded up.

This patch is needed in conjunction with previous commit - 5f1fff1849285f46cfaffadff0352cf976ea4c52

Closes #64
Closes #65