Don't delete unarchived WAL files during crash recovery.

Bug reported by Jehan-Guillaume (ioguix) de Rorthais. This was introduced
with the change to keep WAL files restored from archive in pg_xlog, in 9.2.
Remove VM scannability testing from front of InitPlan.

Preparation for separating scannability from rule expansion for
materialized views.  Conflating makes things rather fragile.
Force archive_status of .done for xlogs created by dearchival/replication.

This is a forward-patch of commit 6f4b8a4f4f7a2d683ff79ab59d3693714b965e3d,
applied to 9.2 back in August. The plan was to do something else in master,
but it looks like it's not going to happen, so let's just apply the 9.2
solution to master as well.

Fujii Masao
Add back ExecCheckRelationsScannable() and call after locks are acquired.

Per suggestion of Noah Misch.
Better fix for "unarchived WAL files get deleted on crash recovery" bug.

Revert my earlier fix for the bug that unarchived WAL files get deleted on
crash recovery, commit c9cc7e05c6d82a9781883a016c70d95aa4923122. We create
a .done file for files streamed or restored from archive, so the WAL file
recycling logic used during normal operation works just as well during
archive recovery.

Per Fujii Masao's suggestion.
Merge branch 'master' of /home/kgrittn/pg/postgresql into matview