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
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present