pgsql: Improvements from Heikki Linnakangas

Log Message:
-----------
Improvements from  Heikki Linnakangas <heikki@enterprisedb.com>

- change the alignment requirement of lexemes in TSVector slightly.
Lexeme strings were always padded to 2-byte aligned length to make sure
that if there's position array (uint16[]) it has the right alignment.
The patch changes that so that the padding is not done when there's no
positions. That makes the storage of tsvectors without positions
slightly more compact.

- added some #include "miscadmin.h" lines I missed in the earlier when I
added calls to check_stack_depth().

- Reimplement the send/recv functions, and added a comment
above them describing the on-wire format. The CRC is now recalculated in
tsquery as well per previous discussion.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        tsginidx.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsginidx.c?r1=1.2&r2=1.3)
        tsquery.c (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery.c?r1=1.4&r2=1.5)
        tsquery_cleanup.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_cleanup.c?r1=1.3&r2=1.4)
        tsquery_rewrite.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_rewrite.c?r1=1.3&r2=1.4)
        tsquery_util.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsquery_util.c?r1=1.3&r2=1.4)
        tsrank.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsrank.c?r1=1.3&r2=1.4)
        tsvector.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsvector.c?r1=1.3&r2=1.4)
        tsvector_op.c (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsvector_op.c?r1=1.3&r2=1.4)
    pgsql/src/include/tsearch:
        ts_type.h (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/tsearch/ts_type.h?r1=1.3&r2=1.4)