Infer a --repository argument from command arguments when reasonable. In particular: if invoked without -R from a CWD not inside a repo, having been passed one or more file paths as command arguments, where the nearest enclosing repo of all of those paths is the same, quietly infer a -R option for that repo. Otherwise abort with an error message as before.

hgweb: separate protocol calls from interface calls (issue996) The protocol functions are already pretty careful about not raising exceptions to the caller, and have their own error handling. We can formalize this a little bit to make it clearer (before, the exception handlers for a limited number of exceptions coming from the interface bits would blow up because some variables aren't instantiated for the protocol calls).