Fix for a weird pthread_rwlock_xxx issue on Mac

[nirbhayc]

On Macbook, the DROP TABLE in the following sequence of commands could randomly hang while trying to acquire write lock on dbtable->sc_live_lk.

create table test(i int)$$
alter table test { schema { cstring i[5] }}$$
drop table test;

In this experimental fix I tried to copy and restore the sc_live_lk from the original table.

This issue was reported by @zevbo.

Signed-off-by: Nirbhay Choubey [email protected]