Force TechRacer maps when image map is selected. Fixes
Google Code issue #882
If you start a TechRacer map with an image map selected, the resulting map will likely to be completely unplayable.
So this commit disables this.
[patterns]
**.h = native
**.c = native
**.cpp = native
**.lua = native
**.txt = native
**.pas = native
**.inc = native
**.hs = native