[PATCH 7 of 8 RFC] context: add isbinary function

[Matt Mackall]

On Wed, 2011-12-21 at 20:45 +0100, Laurens Holst wrote:
> # HG changeset patch
> # User Laurens Holst <laurens.hg at grauw.nl>
> # Date 1324488015 -3600
> # Node ID f6232f3261c0843c78c4283974bf05b5ebff6016
> # Parent  d9641cafc0a939c15b2dec11c8412cea74a90482
> context: add isbinary function

I would have queued this without the rest but it causes conflicts. Put
the easy bits first, please.

-- 
Mathematics is the supreme nostalgia of our time.