(svn r11433) -Fix: starting OpenTTD with DOS files made it look weird out of the box.
-Change: make extra sprites (the ones not in the TTD GRFs) replaceable using Action 5.
-Feature: make replacing contiguous subsets of sprites in for some types possible in Action 5.
Note to GRF authors: when you replaced OpenTTD sprites that are not from the TTD GRF files using Action A, your GRF will not have the intended result anymore as the sprite numbers have changed. You should replace the Action A with an Action 5 from now on.