pgsql: Various fixes for the SGML docs.

Log Message:
-----------
Various fixes for the SGML docs. Consistently use spaces before/after
parentheses in syntax descriptions. Consistently use the present tense
when describing the basic purpose of each "DROP" command. Add a few
more hyperlinks.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        catalogs.sgml (r2.151 -> r2.152)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml.diff?r1=2.151&r2=2.152)
    pgsql/doc/src/sgml/ref:
        alter_index.sgml (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/alter_index.sgml.diff?r1=1.12&r2=1.13)
        analyze.sgml (r1.21 -> r1.22)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/analyze.sgml.diff?r1=1.21&r2=1.22)
        close.sgml (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/close.sgml.diff?r1=1.25&r2=1.26)
        drop_aggregate.sgml (r1.30 -> r1.31)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_aggregate.sgml.diff?r1=1.30&r2=1.31)
        drop_domain.sgml (r1.17 -> r1.18)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_domain.sgml.diff?r1=1.17&r2=1.18)
        drop_language.sgml (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_language.sgml.diff?r1=1.25&r2=1.26)
        drop_sequence.sgml (r1.26 -> r1.27)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_sequence.sgml.diff?r1=1.26&r2=1.27)
        drop_table.sgml (r1.26 -> r1.27)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_table.sgml.diff?r1=1.26&r2=1.27)
        drop_trigger.sgml (r1.21 -> r1.22)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_trigger.sgml.diff?r1=1.21&r2=1.22)
        drop_type.sgml (r1.29 -> r1.30)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/drop_type.sgml.diff?r1=1.29&r2=1.30)
        execute.sgml (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/execute.sgml.diff?r1=1.14&r2=1.15)
        pg_restore.sgml (r1.70 -> r1.71)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_restore.sgml.diff?r1=1.70&r2=1.71)
        prepare.sgml (r1.22 -> r1.23)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/prepare.sgml.diff?r1=1.22&r2=1.23)
        select.sgml (r1.99 -> r1.100)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/select.sgml.diff?r1=1.99&r2=1.100)