pgsql: Add GIN support for pg_trgm.

Log Message:
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Add GIN support for pg_trgm. From Guillaume Smet <guillaume.smet@gmail.com>
with minor editorization by me.

Modified Files:
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    pgsql/contrib/pg_trgm:
        Makefile (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/Makefile.diff?r1=1.6&r2=1.7)
        README.pg_trgm (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/README.pg_trgm.diff?r1=1.2&r2=1.3)
        pg_trgm.sql.in (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/pg_trgm.sql.in.diff?r1=1.2&r2=1.3)
        trgm.h (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/trgm.h.diff?r1=1.6&r2=1.7)
        uninstall_pg_trgm.sql (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/uninstall_pg_trgm.sql.diff?r1=1.2&r2=1.3)
    pgsql/contrib/pg_trgm/expected:
        pg_trgm.out (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/expected/pg_trgm.out.diff?r1=1.1&r2=1.2)
    pgsql/contrib/pg_trgm/sql:
        pg_trgm.sql (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/sql/pg_trgm.sql.diff?r1=1.1&r2=1.2)

Added Files:
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    pgsql/contrib/pg_trgm:
        trgm_gin.c (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/trgm_gin.c?rev=1.1&content-type=text/x-cvsweb-markup)