[PATCH 2 of 3 V4] context: add a `blockancestors(fctx, fromline, toline)` function

[Yuya Nishihara]

On Wed, 04 Jan 2017 17:03:48 +0100, Denis Laxalde wrote:
> # HG changeset patch
> # User Denis Laxalde <denis.laxalde at logilab.fr>
> # Date 1482962617 -3600
> #      Wed Dec 28 23:03:37 2016 +0100
> # Node ID ae66a9ae337e267ecb47f8e2610c308fd81743b7
> # Parent  7f94fa66ee380f223e4790129ff3bd03884b4a26
> # EXP-Topic linerange-log/revset
> context: add a `blockancestors(fctx, fromline, toline)` function
> 
> This yields ancestors of `fctx` by only keeping changesets touching the file
> within specified linerange = (fromline, toline).
> 
> The algorithm is currently limited to following only the first parent in case
> of merge (might be improved later).

So this version appears to support merge revisions, right? I'll remove this
paragraph. Other than that, this patch looks good.