pgsql: Pin the built-in index access methods.

Pin the built-in index access methods.

This was overlooked in commit 473b93287, which introduced DROP ACCESS
METHOD.  Although that command is restricted to superusers, we don't want
even superusers dropping the built-in methods; "DROP ACCESS METHOD btree"
in particular is unrecoverable from.  Pin these objects in the same way
that other initdb-created objects are pinned.

I chose to bump catversion for this fix.  That's not absolutely necessary
perhaps, but it will ensure that no 9.6 production systems are missing
the pin entries.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/16ea51a263bfbb009ba73f36494f49246933e93c

Modified Files
--------------
src/bin/initdb/initdb.c          | 2 ++
src/include/catalog/catversion.h | 2 +-
2 files changed, 3 insertions(+), 1 deletion(-)