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