amend: Fix last-touched when deleting files

[jerry-skydio]

Previously deleted files were not affected by this replay
logic because they don't show up in the new index.

Fix this by adding the old version of the deleted file to
the base of the merge, so the merge-tree will treat it as
deleted. Add a test for this.

[jerry-skydio]

Reviews in this chain:
└#276 amend: Fix last-touched when deleting files
　└#284 git: Use -z for null separated parsing

[jerry-skydio]

#	head	base	diff	date	summary
0	e70a81fe	d9e4421c	diff	Jul 23 16:01 PM	3 files changed, 69 insertions(+), 11 deletions(-)
1	f5bb77dd	f3120035	rebase	Jul 27 13:47 PM	0 files changed
2	fa73cdf5	d6fce997	diff	Jul 27 13:52 PM	3 files changed, 8 insertions(+), 37 deletions(-)
3	258238bd	fa6fd31b	diff	Jul 27 13:54 PM	1 file changed, 20 deletions(-)