pgsql: Improving various checks by Heikki Linnakangas

Log Message:
-----------
Improving various checks by Heikki Linnakangas <heikki@enterprisedb.com>

- add code to check that the query tree is well-formed. It was indeed
  possible to send malformed queries in binary mode, which produced all
  kinds of strange results.

- make the left-field a uint32. There's no reason to
  arbitrarily limit it to 16-bits, and it won't increase the disk/memory
  footprint either now that QueryOperator and QueryOperand are separate
  structs.

- add check_stack_depth() call to all recursive functions I found.
  Some of them might have a natural limit so that you can't force
  arbitrarily deep recursions, but check_stack_depth() is cheap enough
  that seems best to just stick it into anything that might be a problem.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        tsquery.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery.c?r1=1.3&r2=1.4)
        tsquery_cleanup.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_cleanup.c?r1=1.2&r2=1.3)
        tsquery_rewrite.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_rewrite.c?r1=1.2&r2=1.3)
        tsquery_util.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_util.c?r1=1.2&r2=1.3)
        tsrank.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsrank.c?r1=1.2&r2=1.3)
    pgsql/src/include/tsearch:
        ts_type.h (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/tsearch/ts_type.h?r1=1.2&r2=1.3)