There are places in the code that use localrepository.baseui (see hg.remoteui),
we need the ui descriptors (and possibly other things) to be set
correctly on it, so output written to the remoteui descriptors ends up at the
right place.
Before this change, tests such as 'test-bookmarks-pushpull.t' didn't work.
This is a guaranteed by the protocol: clients know they need to read one chunk
off of the 'o' channel and treat that as the hello message.
They should ignore fields they don't recognize so they stay compatible with
new versions of the server in case we decide to add something.
No real reason for a client to do this, but still possible.
Previously if the client sent no arguments, a list with an empty string ['']
would be used as the arguments to dispatch, which would cause hg to complain
about an ambiguous command.
Instead, we simply check for no arguments and use an empty list instead (which
is equivalent to invoking hg with no args on the command line).
