Callback: Show additional text in fund/building window

Show additional text in fund/building window (38/15C)

This callback allows you to display extra information in the industry fund and object building windows. The return value should be the number of a D0xx text to be displayed. The text must begin with a colouring special character and should not be longer than three lines (automatic line breaks are provided, but you can use char 0D for a manual line break). Since the industry isn't built yet, you can't access any industry variables during this callback. Same holds for objects.

Since OpenTTD r20086 and TTDPatch r2354, the contents of registers 100h..105h are copied onto the text reference stack.