copies: eliminate criss-crosses when chaining
Before the copies refactoring, we declared that if a and b were
present in source and destination, we ignored copies between them. The
refactored code could however report b was a copy of a and vice versa
in a situation where we looked for differences between two identical
changesets that copy a to b.
y
/
x
\
y'
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda