reduce construction yard cooldown to 3 seconds

While not crucial, the extra second kind of is annoying and gets in the way of gameplay.
changed nuke launch sound

Someone complained that there was not good warning for the nuke. All you heard was the launch sound, which wasn't that noticeable and a bit like other sounds.
Now it says, "nuclear missile approaching".
Merge pull request #3246 from psydev/cnc

cnc touch-ups