pgsql: Remove use of '<' and '>' in SGML, use '&' escapes.

Log Message:
-----------
Remove use of '<' and '>' in SGML, use '&' escapes.

Update find_gt_lt to allow grep parameters to be passed into it.

Modified Files:
--------------
pgsql/doc/src/sgml:
ddl.sgml (r1.64 -> r1.65)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml.diff?r1=1.64&amp;r2=1.65)
plpython.sgml (r1.33 -> r1.34)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/plpython.sgml.diff?r1=1.33&amp;r2=1.34)
pgsql/doc/src/sgml/ref:
create_opclass.sgml (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_opclass.sgml.diff?r1=1.17&amp;r2=1.18)
pgsql/src/tools:
find_gt_lt (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/find_gt_lt.diff?r1=1.2&amp;r2=1.3)