pgsql: Prevent the unnecessary creation of .ready file for the timeline

Prevent the unnecessary creation of .ready file for the timeline history file.

Previously .ready file was created for the timeline history file at the end
of an archive recovery even when WAL archiving was not enabled.
This creation is unnecessary and causes .ready file to remain infinitely.

This commit changes an archive recovery so that it creates .ready file for
the timeline history file only when WAL archiving is enabled.

Backpatch to all supported versions.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/3a3b7e316f85566771d3a28ea874e030fb12126b

Modified Files
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src/backend/access/transam/timeline.c |    8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)