wireproto: add media type to version 2 capabilities response This is useful to advertise because servers reject unsupported media types. A client may wish to speak multiple media types and choose the one the server supports. I doubt we'll ever use multiple media types or negotiation in core. But during the course of developing this protocol, I may end up making extensions that backport and forward port protocol support as needed to support Mercurial deploys in the wild. e.g. I may deploy support for an older protocol on a server so old clients can continue using it. It's worth pursuing changing the SSH protocol's upgrade mechanism to support multiple media types as well... Differential Revision: https://phab.mercurial-scm.org/D3299

--- a/mercurial/help/internals/wireprotocol.txt	Fri Apr 13 12:31:34 2018 -0700
+++ b/mercurial/help/internals/wireprotocol.txt	Fri Apr 13 12:31:56 2018 -0700
@@ -1770,6 +1770,10 @@
       name
          Name of the compression engine. e.g. ``zstd`` or ``zlib``.
 
+framingmediatypes
+   An array of bytestrings defining the supported framing protocol
+   media types. Servers will not accept media types not in this list.
+
 heads
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