pgsql: Fix up some problems in handling of zic-style time zone names in

Log Message:
-----------
Fix up some problems in handling of zic-style time zone names in datetime
input routines.  Remove the former "DecodePosixTimezone" function in favor of
letting the zic code handle POSIX-style zone specs (see tzparse()).  In
particular this means that "PST+3" now means the same as "-03", whereas it
used to mean "-11" --- the zone abbreviation is effectively just a noise word
in this syntax.  Make sure that all named and POSIX-style zone names will be
parsed as a single token.  Fix long-standing bogosities in printing and input
of fractional-hour timezone offsets (since the tzparse() code will accept
these, we'd better make 'em work).  Also correct an error in the original
coding of the zic-zone-name patch: in "timestamp without time zone" input,
zone names are supposed to be allowed but ignored, but the coding was such
that the zone changed the interpretation anyway.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        datatype.sgml (r1.177 -> r1.178)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml.diff?r1=1.177&r2=1.178)
        datetime.sgml (r2.54 -> r2.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datetime.sgml.diff?r1=2.54&r2=2.55)
    pgsql/src/backend/utils/adt:
        datetime.c (r1.172 -> r1.173)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/datetime.c.diff?r1=1.172&r2=1.173)
    pgsql/src/test/regress/expected:
        horology.out (r1.62 -> r1.63)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/horology.out.diff?r1=1.62&r2=1.63)
        timestamp.out (r1.30 -> r1.31)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamp.out.diff?r1=1.30&r2=1.31)
        timestamptz.out (r1.20 -> r1.21)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamptz.out.diff?r1=1.20&r2=1.21)
    pgsql/src/test/regress/sql:
        timestamp.sql (r1.16 -> r1.17)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/timestamp.sql.diff?r1=1.16&r2=1.17)
        timestamptz.sql (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/timestamptz.sql.diff?r1=1.9&r2=1.10)