Add support for the COMMENT field in DBForge and MySQL Forge classes (pdo, mysql, and mysqli)

Signed-off-by: Zachary Flower <zach@ninjaninja.net>
diff --git a/system/database/DB_forge.php b/system/database/DB_forge.php
index aa8bbbe..df3b90b 100644
--- a/system/database/DB_forge.php
+++ b/system/database/DB_forge.php
@@ -156,6 +156,13 @@
 	 */
 	protected $_default		= ' DEFAULT ';
 
+	/**
+	 * COMMENT value representation in CREATE/ALTER TABLE statements
+	 *
+	 * @var	string
+	 */
+	protected $_comment		= ' COMMENT ';
+
 	// --------------------------------------------------------------------
 
 	/**
@@ -849,6 +856,7 @@
 			.$field['default']
 			.$field['null']
 			.$field['auto_increment']
+			.$field['comment']
 			.$field['unique'];
 	}
 
@@ -987,6 +995,28 @@
 	// --------------------------------------------------------------------
 
 	/**
+	 * Field attribute COMMENT
+	 *
+	 * @param	array	&$attributes
+	 * @param	array	&$field
+	 * @return	void
+	 */
+	protected function _attr_comment(&$attributes, &$field)
+	{
+		if ($this->_comment === FALSE)
+		{
+			return;
+		}
+
+		if (!empty($attributes['COMMENT']))
+		{	
+			$field['comment'] = $this->_default.$this->db->escape($attributes['COMMENT']);
+		}
+	}
+
+	// --------------------------------------------------------------------
+
+	/**
 	 * Process primary keys
 	 *
 	 * @param	string	$table	Table name
diff --git a/system/database/drivers/mysql/mysql_forge.php b/system/database/drivers/mysql/mysql_forge.php
index 6f0d6c5..7053fa1 100644
--- a/system/database/drivers/mysql/mysql_forge.php
+++ b/system/database/drivers/mysql/mysql_forge.php
@@ -192,6 +192,7 @@
 			.$field['null']
 			.$field['default']
 			.$field['auto_increment']
+			.$field['comment']
 			.$field['unique']
 			.$extra_clause;
 	}
diff --git a/system/database/drivers/mysqli/mysqli_forge.php b/system/database/drivers/mysqli/mysqli_forge.php
index c9a5b6d..c92d222 100644
--- a/system/database/drivers/mysqli/mysqli_forge.php
+++ b/system/database/drivers/mysqli/mysqli_forge.php
@@ -194,6 +194,7 @@
 			.$field['null']
 			.$field['default']
 			.$field['auto_increment']
+			.$field['comment']
 			.$field['unique']
 			.$extra_clause;
 	}
diff --git a/system/database/drivers/pdo/subdrivers/pdo_mysql_forge.php b/system/database/drivers/pdo/subdrivers/pdo_mysql_forge.php
index 6cdfcab..85b6ebe 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_mysql_forge.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_mysql_forge.php
@@ -206,6 +206,7 @@
 			.$field['null']
 			.$field['default']
 			.$field['auto_increment']
+			.$field['comment']
 			.$field['unique']
 			.$extra_clause;
 	}