Add experimental support for a total hit count in the MySQL search engine.

Add experimental support for a total hit count in the MySQL search engine.
Disabled by default as it's a bit flaky when you combine title and page content results... also might be slow on larger sites. :)
Good for local UI testing to confirm that the search count totals work in the search UI/API though!

/**
 * Set to true to have the default MySQL search engine count total
 * search matches to present in the Special:Search UI.
 *
 * This could however be slow on larger wikis, and is pretty flaky
 * with the current title vs content split. Recommend avoiding until
 * that's been worked out cleanly; but this may aid in testing the
 * search UI and API to confirm that the result count works.
 */
$wgSearchMySQLTotalHits = false;