amend: rectify comment Comment was ambiguous as there can be two parents of a changeset in mercurial. This commit fixes the comment to clarify that the first parent is being considered. Test Plan: ran the test suite Differential Revision: https://phab.mercurial-scm.org/D595

amend: removing redundant if condition There is needless checking for the new commit hash not being equal to the old commit hash. This condition will always be true at this point in the code path and thus, can be removed safely. This commit removes the redundant condition. Test Plan: ran the test suite. Differential Revision: https://phab.mercurial-scm.org/D594

editor: file created for diff action should have .diff suffix This is a follow-up to https://phab.mercurial-scm.org/D464 (6e6452bc441d) that introduced the new file extension behavior. It erroneously changed `.diff` to `.diff.hg.txt`. Test Plan: Verified `make tests` passes, particularly `test-editor-filename.t`. Differential Revision: https://phab.mercurial-scm.org/D607