Description
bool 
imap_reopen ( resource imap_stream, string mailbox [, string options])
  
     This function reopens the specified stream to a new 
     mailbox on an IMAP or NNTP server.
    
     The options are a bit mask with one or more of the following:
     
- 
        OP_READONLY - Open mailbox read-only
        
- 
        OP_ANONYMOUS - Don't use or update a
        .newsrc for news (NNTP only)
        
- 
        OP_HALFOPEN - For IMAP and NNTP names, open a connection but
        don't open a mailbox.
        
- 
        CL_EXPUNGE - Expunge mailbox automatically upon mailbox close
        (see also imap_delete() and
        imap_expunge())
        
     如果成功则返回 TRUE,失败则返回 FALSE。