pgsql: Retry opening new segments in pg_xlogdump --folllow

Retry opening new segments in pg_xlogdump --folllow

There is a small window between when the server closes out the existing
segment and the new one is created. Put a loop around the open call in
this case to make sure we wait for the new file to actually appear.

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/d8b4c3490c8ada0e39727475328a67c2e510f2f2

Modified Files
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src/bin/pg_xlogdump/pg_xlogdump.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)