pgsql: Mark correctly initial slot snapshots with MVCC type when built

Mark correctly initial slot snapshots with MVCC type when built

When building an initial slot snapshot, snapshots are marked with
historic MVCC snapshots as type with the marker field being set in
SnapBuildBuildSnapshot() but not overriden in SnapBuildExportSnapshot().
Existing callers of SnapBuildBuildSnapshot() do not care about the type
of snapshot used, but extensions calling it actually may, as reported.

Author: Antonin Houska
Reviewed-by: Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/23215.1527665193@localhost
Backpatch-through: 9.4

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2ad57e9e9faf5e8a6fdec048636581df7210478f

Modified Files
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src/backend/replication/logical/snapbuild.c | 2 ++
1 file changed, 2 insertions(+)