hghave: avoid a deadlock reading the child process's output
The output of `pylint` is voluminous enough that it fills the buffer on Windows,
and waited for the parent to read it out. But the parent was waiting on the
child to exit.
I'm not sure what the intent of setting `ret = -1` in the exception handler just
above this was...
Just exercise debugindexdot
Create a short file history including a merge.
$ hg init t
$ cd t
$ echo a > a
$ hg ci -qAm t1 -d '0 0'
$ echo a >> a
$ hg ci -m t2 -d '1 0'
$ hg up -qC 0
$ echo b >> a
$ hg ci -m t3 -d '2 0'
created new head
$ HGMERGE=true hg merge -q
$ hg ci -m merge -d '3 0'
$ hg debugindexdot a
digraph G {
-1 -> 0
0 -> 1
0 -> 2
2 -> 3
1 -> 3
}
$ cd ..