requirements: introduce a set of working directory specific requirements
Some requirements like the SPARSE_REQUIREMENT is working directory specific and
cannot be shared. We add a set which will contain all these requirements.
This is not the best we can do, I think having a rich requirement class will be
much better but that will be out of scope for this series.
Differential Revision: https://phab.mercurial-scm.org/D8924
$ 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 ..