More message editing, some suggested by Alvaro Herrera

src/backend/catalog/index.c

src/backend/catalog/pg_proc.c

src/backend/commands/dbcommands.c

src/backend/commands/functioncmds.c

src/backend/commands/indexcmds.c

src/backend/commands/tablecmds.c

src/backend/commands/typecmds.c

src/backend/commands/user.c

src/backend/commands/vacuum.c

src/backend/parser/parse_coerce.c

src/backend/parser/parse_func.c

src/backend/port/sysv_shmem.c

src/backend/rewrite/rewriteDefine.c

src/backend/storage/freespace/freespace.c

src/backend/storage/page/bufpage.c

src/backend/tcop/postgres.c

src/backend/utils/adt/formatting.c

src/backend/utils/adt/geo_ops.c

src/backend/utils/adt/mac.c

src/backend/utils/adt/nabstime.c