The previous commit taught hg.clone() to define a creation option
when file include or exclude patterns are passed.
This commit teaches the new repo creation code to convert that creation
option into a repository requirement.
While not yet used by the narrow extension, the eventual side-effect
of this change is that newly-created repositories will have the narrow
requirement from their creation onset. Currently, the requirement is
added to the repo at exchange.pull() time via a wrapped function in
the narrow extension.