sparse: add test showing `hg merge` is broken while using sparse extension
This patch adds a test to demonstrate that `hg merge` is broken in some cases
while using sparse extension.
The case is when you have a file which is:
* modified between current wdir parent and merge base
* deleted between merge base and merge destination
* excluded from sparse checkout
Doing `hg merge` results in file not found error. Next patch will fix this.
Differential Revision: https://phab.mercurial-scm.org/D3983
$ 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 ..