update various docs to use DB:expr() properly (refs #4617)

Author: zeelot

classes/Kohana/Database.php

@@ -485,8 +485,7 @@ public function quote($value)
 	 *
 	 * You can also use SQL methods within identifiers.
 	 *
-	 *     // The value of "column" will be quoted
-	 *     $column = $db->quote_column('COUNT("column")');
+	 *     $column = $db->quote_column(DB::expr('COUNT(`column`)'));
 	 *
 	 * Objects passed to this function will be converted to strings.
 	 * [Database_Expression] objects will be compiled.

guide/database/examples.md

@@ -25,7 +25,7 @@ In this example, we loop through an array of whitelisted input fields and for ea
 
 	//copy the query & execute it
 	$pagination_query = clone $query;
-	$count = $pagination_query->select('COUNT("*") AS mycount')->execute()->get('mycount');
+	$count = $pagination_query->select(DB::expr('COUNT(*)) AS mycount')->execute()->get('mycount');
 
 	//pass the total item count to Pagination
 	$config = Kohana::$config->load('pagination');

guide/database/results.md

@@ -70,7 +70,7 @@ To return a non-associative array, leave `$key` as NULL and just pass a `$value`
 
 Sometime you only want a single value from a query. The `get()` method returns the value of the named column from the current row. The second parameter, `$default`, is used to supply a default value when the result is NULL.
 
-	$total_users = DB::select(array('COUNT("username")', 'total_users'))->from('users')->execute()->get('total_users', 0);
+	$total_users = DB::select(array(DB::expr('COUNT(`username`)'), 'total_users'))->from('users')->execute()->get('total_users', 0);
 
 ### Select - `cached()`