[YSQL] Warning: leaking still-referenced relcache entry

[m-iancu]

Can happen for some mixes DMLs with DDLs from multiple connections.
To replicate:

1. start two connections at the same time with :

./bin/psql -h 127.0.0.1 -p 5433 -U postgres

2. In connection 1 run:

postgres=# create table test2 (b int);
CREATE TABLE

3. in connection 2:

postgres=#  insert into test2(non_existent_column) values (1);
WARNING:  leaking still-referenced relcache entry for "test2"
ERROR:  column "non_existent_column" of relation "test2" does not exist
LINE 1: insert into test2(non_existent_column) values (1);

[m-iancu]

Closed in 465b6d6.