Use $current_site->path instead of $base in wpmu_validate_blog_signup(), as...

Use $current_site->path instead of $base in wpmu_validate_blog_signup(), as $base is now dead. props MarkJaquith. fixes #22787. see #19796.



git-svn-id: https://core.svn.wordpress.org/trunk@23107 1a063a9b-81f0-0310-95a4-ce76da25c4cd