pgsql: Fix the size of predicate lock manager's shared memory hash tabl

Fix the size of predicate lock manager's shared memory hash tables at creation.

This way they don't compete with the regular lock manager for the slack shared
memory, making the behavior more predictable.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/7c797e7194d969f974abf579cacf30ffdccdbb95

Modified Files
--------------
src/backend/storage/lmgr/predicate.c |   22 +++++++++-------------
src/backend/utils/hash/dynahash.c    |    6 ++++++
src/include/utils/hsearch.h          |    1 +
3 files changed, 16 insertions(+), 13 deletions(-)