Fix Dataset#limit on MSSQL 2000

This was broken when support to allow limit to be a bound variable
was added.  Now Sequel will use TOP(N) for MSSQL 2000, and TOP (N)
for MSSQL 2005+.  Tested on MSSQL 2000 and MSSQL 2008.

lib/sequel/adapters/shared/mssql.rb

@@ -430,9 +430,14 @@ def select_into_sql(sql)
         sql << " INTO #{table_ref(@opts[:into])}" if @opts[:into]
       end
 
-      # MSSQL uses TOP for limit
+      # MSSQL uses TOP N for limit.  For MSSQL 2005+ TOP (N) is used
+      # to allow the limit to be a bound variable.
       def select_limit_sql(sql)
-        sql << " TOP (#{literal(@opts[:limit])})" if @opts[:limit]
+        if l = @opts[:limit]
+          l = literal(l)
+          l = "(#{l})" if server_version >= 9000000
+          sql << " TOP #{l}"
+        end
       end
 
       # Support different types of locking styles