search-replace: whitespace fixes
search-replace: blacklist user_pass column later
search-replace: extract get_table_list() method
search-replace: fix warning from using wpdb->prepare() with only 1 parameter
search-replace: use a single SHOW TABLES query to get list of multisite tables

Besides simplicity, it avoids warnings for non-existant tables.

For example, the Posts 2 Posts plugin creates 2 custom, per-blog tables.
But it might not be activated on all blogs.