Add short description, reindent long description

Fixes the following lintian warnings:

* description-starts-with-package-name
* description-synopsis-might-not-be-phrased-properly
* description-too-long (refers to first line)
* extended-description-is-empty
"Add "set -e" to postinst script to bail out on any error

Fixes lintian warning maintainer-script-ignores-errors