Clean up some aspects of pg_dump/pg_restore item-selection logic.

Clean up some aspects of pg_dump/pg_restore item-selection logic.

Ensure that CREATE DATABASE and related commands are issued when, and
only when, --create is specified.  Previously there were scenarios
where using selective-dump switches would prevent --create from having
any effect.  For example, it would fail to do anything in pg_restore
if the archive file had been made by a selective dump, because there
would be no TOC entry for the database.

Since we don't issue \connect either if we don't issue CREATE DATABASE,
this could result in unexpectedly restoring objects into the wrong
database.

Also fix pg_restore's selective restore logic so that when an object is
selected to be restored, we also restore its ACL, comment, and security
label if any.  Previously there was no way to get the latter properties
except through tedious mucking about with a -L file.  If, for some
reason, you don't want these properties, you can match the old behavior
by adding --no-acl etc.

While at it, try to make _tocEntryRequired() a little better organized
and better documented.

Discussion: https://postgr.es/m/32668.1516848577@sss.pgh.pa.us