Add slack-desc_check.sh.

Signed-off-by: David Spencer <baildon.research@googlemail.com>
Fix slack-desc_check.sh for review comments.

Add copyright line.
Simplify check on number of description lines.
Don't obsess over the handy ruler.

Signed-off-by: David Spencer <baildon.research@googlemail.com>
Add new checks.

install-dir_check.sh
ownership_check.sh
symlink_check.sh
tar113_check.sh

Signed-off-by: David Spencer <baildon.research@googlemail.com>