No longer use native autoreconnection in the mysql adapter

Native autoreconnection has problems with prepared statements, where
a new native connection is used behind Sequel's back, so Sequel
thinks the prepared statement has already been defined on the
connection, when it fact it hasn't.  Any other changes that affect
the state of the connection will be lost when native autoreconnection
is used as well.

Sequel's connection pool already handles reconnection if it detects a
disconnection.  This commit also adds an additional exception message
to recognize as a disconnect.

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* No longer use native autoreconnection in the mysql adapter (jeremyevans)
+
 * Add NULL, NOTNULL, TRUE, SQLTRUE, FALSE, and SQLFALSE constants (jeremyevans)
 
 * Add Dataset #select_map, #select_order_map, and #select_hash (jeremyevans)

lib/sequel/adapters/mysql.rb

@@ -70,7 +70,7 @@ class Database < Sequel::Database
       include Sequel::MySQL::DatabaseMethods
 
       # Mysql::Error messages that indicate the current connection should be disconnected
-      MYSQL_DATABASE_DISCONNECT_ERRORS = /\A(Commands out of sync; you can't run this command now\z|Can't connect to local MySQL server through socket)/
+      MYSQL_DATABASE_DISCONNECT_ERRORS = /\A(Commands out of sync; you can't run this command now|Can't connect to local MySQL server through socket|MySQL server has gone away)/
 
       set_adapter_scheme :mysql
 
@@ -124,7 +124,6 @@ class << conn
           attr_accessor :prepared_statements
         end
         conn.prepared_statements = {}
-        conn.reconnect = true
         conn
       end