Added support for bogo-logins.

Added support for bogo-logins.
One can now "login" using any WikiWord as a user ID.
(Unless logging in as the admin user, any password will work.)

Currently, the sole effect of logging in is that the
the logged-in user ID is recorded as the author of any
page edits.  Thus, "logging in" allows one to control
the author which appears in RecentChanges and the page
info display.

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@531 96ab9672-09ca-45d6-a79d-3d69d39ca109