Don't delete non-block edges unless they're at the top of a block

Dependencies

• [2] L5PHFTIE Minor simplification
• [*] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• edit in libpijul/src/diff/delete.rs at line 158
  [4.810684]

  [2.0]
  + if graph_key.start != del_key.start && !v.flag.contains(EdgeFlags::BLOCK) {

  + continue

  + }