pgsql: In pg_upgrade, use cached copy of directory listing, rather than

In pg_upgrade, use cached copy of directory listing, rather than calling
scandir() with a pattern for every table.

Optimization after report of pg_upgrade slowness with 150k tables.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=ad06db2610f479d559ee4a3b9e3241d40be07440

Modified Files
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contrib/pg_upgrade/info.c | 15 +++---
contrib/pg_upgrade/pg_upgrade.h | 25 ++++------
contrib/pg_upgrade/relfilenode.c | 88 ++++++++++++++++++++++++--------------
3 files changed, 74 insertions(+), 54 deletions(-)