Fix tar files emitted by pg_basebackup to be POSIX conformant.

Fix tar files emitted by pg_basebackup to be POSIX conformant.

Back-patch portions of commit 05b555d12bc2ad0d581f48a12b45174db41dc10d.
There doesn't seem to be any reason not to fix pg_basebackup fully, but
we can't change pg_dump's "magic" string without breaking older versions
of pg_restore.  Instead, just patch pg_restore to accept either version
of the magic string, in hopes of avoiding compatibility problems when
9.3 comes out.  I also fixed pg_dump to write the correct 2-block EOF
marker, since that won't create a compatibility problem with pg_restore
and it could help with some versions of tar.

Brian Weaver and Tom Lane