Move installation of build dependencies to separate script file.

.travis.yml

@@ -3,11 +3,7 @@ sudo: required
 env:
   - EMULATOR=simh
   - EMULATOR=klh10
-install:
-  - sudo add-apt-repository ppa:dns/gnu -y
-  - sudo apt-get update -myq
-  - sudo apt-get install -my simh expect
-  - sudo apt-get install --only-upgrade autoconf
+install: sh -ex build/dependencies.sh install_${TRAVIS_OS_NAME:-linux}
 script: make
 notifications:
   email: lars@nocrew.org