error out if sql query fails

error out if sql query fails

Using "echo ... | psql" does not generate an error when something goes
wrong.  Using "psql -c ..." instead does:

  $ echo "SELECT * FROM does_not_exist" | psql projectb 2>/dev/null; echo $?
  0

  $ q="SELECT * FROM does_not_exist"; psql -c "$q" projectb 2>/dev/null; echo $?
  1

This patch switches dak to use the second form to avoid silenty ignoring
errors.

Signed-off-by: Ansgar Burchardt <ansgar@debian.org>