When the MySQL server has "gone away," attempt to reconnect and retry the query.

props pento.
see #5932.


git-svn-id: https://develop.svn.wordpress.org/trunk@27075 602fd350-edb4-49c9-b593-d223f7449a82
Remove an unnecessary variable passed to wpdb::prepare() during multisite load.

props jeremyfelt.
fixes #26941.


git-svn-id: https://develop.svn.wordpress.org/trunk@27076 602fd350-edb4-49c9-b593-d223f7449a82
Consistently trim and unslash search queries for the users list tables.

props aubreypwd.
fixes #26115.


git-svn-id: https://develop.svn.wordpress.org/trunk@27077 602fd350-edb4-49c9-b593-d223f7449a82