copies: add a HASCOPIESINFO flag to highlight rev with useful data
If some files changes that may impact copy tracing are detected, we set this
flag. This helps the copy tracing algorithm to skip fetching possibly expensive
data when unnecessary.
Differential Revision: https://phab.mercurial-scm.org/D9139
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..