TABLES" and failures of alter_table.test on Windows which occured after
pushing fix for bugs #20662, #20903, #24508, #24738 (various problems
with CREATE TABLE SELECT).

ALTER TABLE statements which were handled using "fast" alter table
optimization were not properly working under LOCK TABLES if table
was transactional (for all table types under Windows).

Code implementing "fast" version of ALTER TABLE tried to open and
lock table using open_ltable() after renaming .FRM files (which
corresponds to renaming tables in normal case) in some cases
(for transactional tables or on Windows). This caused problems
under LOCK TABLES and conflicted with name-lock taken by 
ALTER TABLE RENAME on target tables.

This patch solves this issue by using reopen_name_locked_table()
instead of open_ltable().