message: Give a more helpful message on error
  Before:
  ```
  database error: ERROR: insert or update on table "owner_rels" violates foreign key constraint "owner_rels_cid_fkey"
  ```
  After:
  ```
  database error: ERROR: insert or update on table "owner_rels" violates foreign key constraint "owner_rels_cid_fkey"
  DETAIL:  Key (cid)=(4) is not present in table "releases".
  ```
diff: @@ -309,7 +309,14 @@ impl DbError {
  impl fmt::Display for DbError {
  fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
  - write!(fmt, "{}: {}", self.severity, self.message)
  + write!(fmt, "{}: {}", self.severity, self.message)?;
  + if let Some(detail) = &self.detail {
  + write!(fmt, "DETAIL: {}", detail)?;
  + }
  + if let Some(hint) = &self.hint {
  + write!(fmt, "HINT: {}", hint)?;
  + }
  + Ok(())
  }
  }
  