ASSERTION TABLE->DB_STAT FAILED IN
SQL_BASE.CC::OPEN_TABLE() DURING I_S Q

This assert could be triggered if a statement requiring a name
lock on a table (e.g. DROP TRIGGER) executed concurrently
with an I_S query which also used the table.

One connection first started an I_S query that opened a given table.
Then another connection started a statement requiring a name lock
on the same table. This statement was blocked since the table was
in use by the I_S query. When the I_S query resumed and tried to
open the table again as part of get_all_tables(), it would encounter
a table instance with an old version number representing the pending
name lock. Since I_S queries ignore version checks and thus pending
name locks, it would try to continue. This caused it to encounter
the assert. The assert checked that the TABLE instance found with a
different version, was a real, open table. However, since this TABLE
instance instead represented a pending name lock, the check would
fail and trigger the assert.

This patch fixes the problem by removing the assert. It is ok for
TABLE::db_stat to be 0 in this case since the TABLE instance can
represent a pending name lock.

Test case added to lock_sync.test.