pgsql: Actually, all of parallel restore's limitations should be tested

Actually, all of parallel restore's limitations should be tested earlier.

On closer inspection, whining in restore_toc_entries_parallel is really
much too late for any user-facing error case. The right place to do it
is at the start of RestoreArchive(), before we've done anything interesting
(suh as trying to DROP all the targets ...)

Back-patch to 8.4, where parallel restore was introduced.

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/4fa37702a041a90355f693e10cad0751ef700658

Modified Files
--------------
src/bin/pg_dump/pg_backup_archiver.c | 38 ++++++++++++++++++++-------------
1 files changed, 23 insertions(+), 15 deletions(-)