Spell checking and markup refinement

doc/src/sgml/backup.sgml

doc/src/sgml/btree-gist.sgml

doc/src/sgml/catalogs.sgml

doc/src/sgml/config.sgml

doc/src/sgml/ecpg.sgml

doc/src/sgml/extend.sgml

doc/src/sgml/file-fdw.sgml

doc/src/sgml/func.sgml

doc/src/sgml/high-availability.sgml

doc/src/sgml/installation.sgml

doc/src/sgml/libpq.sgml

doc/src/sgml/monitoring.sgml

doc/src/sgml/mvcc.sgml

doc/src/sgml/perform.sgml

doc/src/sgml/pgtestfsync.sgml

doc/src/sgml/plperl.sgml

doc/src/sgml/plpgsql.sgml

doc/src/sgml/plpython.sgml

doc/src/sgml/queries.sgml

doc/src/sgml/ref/alter_opfamily.sgml