db.hh: use hasPrefix for prefix comparisons

Dependencies

• [2] OWRS526H Create an ephemeral PostgreSQL database per test
• [3] HJOEIMLR Refactor

Change contents

• replacement in src/libhydra/db.hh at line 20
  [2.96]→[2.96:240](∅→∅)
  − if ((std::string(s, 0, lower_prefix.size()) == lower_prefix) ||

  − (std::string(s, 0, upper_prefix.size()) == upper_prefix)) {
  [2.96]

  [2.240]
  + if (hasPrefix(s, lower_prefix) || hasPrefix(s, upper_prefix)) {