pgsql: Obtain table locks as soon as practical during pg_dump.

Obtain table locks as soon as practical during pg_dump.

For some reason, when we (I) added table lock acquisition to pg_dump,
we didn't think about making it happen as soon as possible after the
start of the transaction. What with subsequent additions, there was
actually quite a lot going on before we got around to that; which sort
of defeats the purpose. Rearrange the order of calls in dumpSchema()
to close the risk window as much as we easily can. Back-patch to all
supported branches.

Branch
------
REL8_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/32e5768390fe7c10230a1d02d9ee026461a609a9

Modified Files
--------------
src/bin/pg_dump/common.c | 16 +++++++++++-----
1 files changed, 11 insertions(+), 5 deletions(-)