pgsql: Clean up cruft around collation initialization for tupdescs and

Clean up cruft around collation initialization for tupdescs and scankeys.

I found actual bugs in GiST and plpgsql; the rest of this is cosmetic
but meant to decrease the odds of future bugs of omission.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/7208fae18f1fdb242b4fcced77a3b836e15ac3ec

Modified Files
--------------
src/backend/access/common/scankey.c | 25 ++++++++++-----------
src/backend/access/common/tupdesc.c | 10 ++++++--
src/backend/access/gin/ginutil.c | 2 +
src/backend/access/gist/gistscan.c | 10 +++++++-
src/backend/access/nbtree/nbtsearch.c | 6 +---
src/backend/access/nbtree/nbtutils.c | 8 +++++-
src/backend/commands/seclabel.c | 3 --
src/backend/commands/sequence.c | 15 ++++++++----
src/backend/executor/nodeIndexscan.c | 10 +++-----
src/backend/executor/nodeMergeAppend.c | 30 ++++++++++++++------------
src/backend/utils/adt/pgstatfuncs.c | 36 +++++++++++++++++++++----------
src/backend/utils/adt/selfuncs.c | 1 +
src/backend/utils/cache/catcache.c | 2 +
src/backend/utils/sort/tuplesort.c | 31 ++++++++++++++-------------
src/include/access/skey.h | 7 ++++-
src/pl/plpgsql/src/pl_comp.c | 4 +++
16 files changed, 119 insertions(+), 81 deletions(-)