Align the spacing of the multisite constants with what has been...

Align the spacing of the multisite constants with what has been long-established in wp-config and wp-config-sample. props ryanduff, fixes #19869.

git-svn-id: https://core.svn.wordpress.org/trunk@19956 1a063a9b-81f0-0310-95a4-ce76da25c4cd