RFR: Make webrev reject positional arguments

[Leo Korinth via github.com]

The pull request has been updated with additional changes.

----------------

Added commits:
 - f94fe989:	Update cli/resources/man/man1/git-webrev.1
			Co-Authored-By: Erik Duveblad <erik.helin at oracle.com>
 - b505f951:	Update cli/resources/man/man1/git-webrev.1
			Co-Authored-By: Erik Duveblad <erik.helin at oracle.com>

Pull request:
https://git.openjdk.java.net/skara/pull/79

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/79/webrev.01
 - inc: https://webrevs.openjdk.java.net/skara/79/webrev.00-01

Updated full patch:
https://git.openjdk.java.net/skara/pull/79.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/79/head:pull/79