HANG

Problem Statement:

When the operation RENAME TABLE is about rename the tablespace of the
table, it will stop all i/o operations on the tablespace temporarily.
For this the fil_space_t::stop_ios member is used.

Once the fil_space_t::stop_ios member is set to TRUE in the RENAME
TABLE operation, it is expected that no new i/o operation will be done
on the tablespace and all pending i/o operation can be completed on
the tablespace.

If the pending i/o operations initiate any new i/o operations then
there will be deadlock.  The RENAME TABLE operation will be waiting
for pending i/o on the tablespace to be completed, and the pending i/o
operations will be waiting on the RENAME TABLE operation to set the
file_space_t::stop_ios flag to be set to FALSE.

But in the given scenario the pending i/o operations did not initiate
new i/o.  But they where still unnecessarily checking the
fil_space_t::stop_ios flag.  This resulted in deadlock.

Solution:

I noticed that this deadlock happens in fil_space_get_size() and
fil_space_get_zip_size() in the i/o threads.  These functions check
the stop_ios flag even when no i/o will be initiated.  I modified
these functions to ensure that they check the stop_ios flag only when
they will be initiating an i/o operation.  This solves the problem.

rb://1635 (mysql-5.5)
rb://1660 (mysql-trunk) approved by Inaam, Jimmy, and ima.