Let table_exists? find tables in @@table_cache even if symbols are passed as their names

lib/arel/table.rb

@@ -8,7 +8,7 @@ class << self; attr_accessor :engine; end
     attr_accessor :name, :engine, :aliases, :table_alias
 
     def initialize name, engine = Table.engine
-      @name    = name
+      @name    = name.to_s
       @engine  = engine
       @columns = nil
       @aliases = []
@@ -22,7 +22,7 @@ def initialize name, engine = Table.engine
         # Sometime AR sends an :as parameter to table, to let the table know
         # that it is an Alias.  We may want to override new, and return a
         # TableAlias node?
-        @table_alias = engine[:as] unless engine[:as].to_s == name.to_s
+        @table_alias = engine[:as] unless engine[:as].to_s == name
       end
     end