after few delete statements

Problem: changing a file size might require that it must be 
unmapped beforehand.
  
Fix: unmap the file before changing its size.


mysql-test/r/temp_table.result:
  Fix for bug #35392: Delete all statement does not execute properly 
  after few delete statements
    - test result.
mysql-test/t/temp_table.test:
  Fix for bug #35392: Delete all statement does not execute properly 
  after few delete statements
    - test case.
storage/myisam/mi_delete_all.c:
  Fix for bug #35392: Delete all statement does not execute properly 
  after few delete statements
    - unmap file before changing its size as it's required 
      by SetEndOfFile() function (see my_chsize()).
    - as no other threads allowed to perform concurrent inserts 
      when delete_all is called, mmap_lock locking removed.