iostream.hpp: Add get(char&) override to allow unpack(fc::istream, unsigned_int)

include/fc/io/iostream.hpp

@@ -31,6 +31,7 @@ namespace fc {
       istream&   read( char* buf, size_t len );
       istream&   read( const std::shared_ptr<char>& buf, size_t len, size_t offset = 0 );
       virtual char get();
+      void get( char& c ) { c = get(); }
   };
   typedef std::shared_ptr<istream> istream_ptr;