pgsql: GIN documentation and slightly improving GiST docs.

Log Message:
-----------
GIN documentation and slightly improving GiST docs.
Thanks to Christopher Kings-Lynne <chris(dot)kingslynne(at)gmail(dot)com> for
initial version and Jeff Davis <pgsql(at)j-davis(dot)com> for inspection

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.85 -> r1.86)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.85&r2=1.86)
filelist.sgml (r1.46 -> r1.47)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/filelist.sgml.diff?r1=1.46&r2=1.47)
geqo.sgml (r1.36 -> r1.37)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/geqo.sgml.diff?r1=1.36&r2=1.37)
indices.sgml (r1.61 -> r1.62)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/indices.sgml.diff?r1=1.61&r2=1.62)
mvcc.sgml (r2.58 -> r2.59)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/mvcc.sgml.diff?r1=2.58&r2=2.59)
xindex.sgml (r1.45 -> r1.46)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/xindex.sgml.diff?r1=1.45&r2=1.46)
pgsql/doc/src/sgml/ref:
create_opclass.sgml (r1.15 -> r1.16)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_opclass.sgml.diff?r1=1.15&r2=1.16)

Added Files:
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pgsql/doc/src/sgml:
gin.sgml (r2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/gin.sgml?rev=2.1&content-type=text/x-cvsweb-markup)