Merge changes made in Emacs trunk.

Merge changes made in Emacs trunk.

proto-stream.el: Changes preparatory to merging open-protocol-stream with open-network-stream.
 (proto-stream-always-use-starttls): Option removed.
 (open-protocol-stream): Return a process object by default.  Provide a new parameter :return-list specifying a list-type return value, which now has the form (PROP . PLIST) instead of a fixed-length list.  Change :type `network' to `try-starttls', and `network-only' to `default'.  Make `default' the default, for compatibility with open-network-stream.  Handle the no-parameter case exactly as open-network-stream, with no additional stream processing.  Search plists using plist-get.  Explicitly add :end-of-commend parameter if it is missing.
 (proto-stream-open-default): Renamed from proto-stream-open-network-only.  Return 'default as the type.
 (proto-stream-open-starttls): Rename from proto-stream-open-network.  Use plist-get.  Don't return `tls' as the type if STARTTLS negotiation failed.  Always return a list with a (possibly dead) process as the first element, for compatibility with open-network-stream.
 (proto-stream-open-tls): Use plist-get.  Always return a list.
 (proto-stream-open-shell): Return `default' as connection type.
 (proto-stream-capability-open): Use plist-get.
 (proto-stream-eoc): Function deleted.
nnimap.el (nnimap-stream, nnimap-open-connection, nnimap-open-connection-1): Handle renaming of :type parameter for open-protocol-stream.
 (nnimap-open-connection-1): Pass a :return-list parameter open-protocol-stream to obtain a list return value.  Parse this list using plist-get.
nntp.el (nntp-open-connection): Handle renaming of :type parameter for open-protocol-stream.  Accept open-protocol-stream return value that is a subprocess object instead of a list.  Handle the case of a dead returned process.