pgsql: Update docs to reflect the fact that we can now deal with DST

Log Message:
-----------
Update docs to reflect the fact that we can now deal with DST rules
outside the 32-bit-time_t range. Also, refer to Olson's tz database
as the 'zoneinfo' database, a name that upstream sometimes uses, not
'zic database' which they never use.

Modified Files:
--------------
pgsql/doc/src/sgml:
datatype.sgml (r1.224 -> r1.225)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml?r1=1.224&r2=1.225)
datetime.sgml (r2.58 -> r2.59)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datetime.sgml?r1=2.58&r2=2.59)
installation.sgml (r1.300 -> r1.301)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.300&r2=1.301)