pgsql: Use memcmp() rather than strncmp() when shorter string length is

Use memcmp() rather than strncmp() when shorter string length is known.

It appears that this will be faster for all but the shortest strings;
at least one some platforms, memcmp() can use word-at-a-time comparisons.

Noah Misch, somewhat pared down.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=32ba2b516066688ff56e6d62a7ff4a01c88f5700

Modified Files
--------------
contrib/hstore/hstore_io.c | 8 ++++----
contrib/hstore/hstore_op.c | 26 +++++++++++++-------------
contrib/ltree/ltree_gist.c | 2 +-
contrib/ltree/ltree_op.c | 8 ++++----
src/backend/nodes/readfuncs.c | 2 +-
src/backend/utils/adt/varchar.c | 6 +++---
src/backend/utils/adt/varlena.c | 14 +++++++-------
7 files changed, 33 insertions(+), 33 deletions(-)