Make .travis.yml directly portable across repos

Didn't test, but should DTRT for self-tests and for other people's repos.
Since script is actually bash, so don't use sh
Merge newest from branch 'luis/master' into patch-1

Conflicts:
	.travis.yml
Add README.md
install.sh is now pure sh
Merge newest from branch 'luis/master' into patch-1
Slightly safer tarball unpacking. Also more helpful message.
Prevent ./install.sh script from running twice

* .travis.yml (install): Prevent script from being run twice if
./install.sh exists but fails for some reason.

* install.sh: Add a signature line indentifying this as the
cl-travis install script.
Improve README.md
Merge pull request #1 from capitaomorte/patch-1

Make .travis.yml directly portable across repos