
new smmu linedef types for script
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        Walk triggers
270             -- WR start script number specified by tag number
271             -- WR as 270 but one-direction only
272             -- W1 as 270
273             -- W1 as 271

274             -- SR start script specified by tag number (switch)
275             -- S1 as 274

276             -- GR start script (shoot)
277             -- G1 as 277


