pgsql: Simplify pg_am representation of ordering-capable access methods:

Log Message:
-----------
Simplify pg_am representation of ordering-capable access methods:
provide just a boolean 'amcanorder', instead of fields that specify the
sort operator strategy numbers.  We have decided to require ordering-capable
AMs to use btree-compatible strategy numbers, so the old fields are
overkill (and indeed misleading about what's allowed).

Modified Files:
--------------
    pgsql/doc/src/sgml:
        catalogs.sgml (r2.141 -> r2.142)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml.diff?r1=2.141&r2=2.142)
        indexam.sgml (r2.19 -> r2.20)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/indexam.sgml.diff?r1=2.19&r2=2.20)
        xindex.sgml (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/xindex.sgml.diff?r1=1.54&r2=1.55)
    pgsql/src/backend/commands:
        indexcmds.c (r1.152 -> r1.153)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/indexcmds.c.diff?r1=1.152&r2=1.153)
    pgsql/src/backend/optimizer/util:
        plancat.c (r1.131 -> r1.132)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/plancat.c.diff?r1=1.131&r2=1.132)
    pgsql/src/backend/utils/adt:
        ruleutils.c (r1.244 -> r1.245)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ruleutils.c.diff?r1=1.244&r2=1.245)
    pgsql/src/include/catalog:
        catversion.h (r1.374 -> r1.375)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.374&r2=1.375)
        pg_am.h (r1.49 -> r1.50)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_am.h.diff?r1=1.49&r2=1.50)