Message style improvements

src/backend/access/gin/ginarrayproc.c

src/backend/access/gin/ginscan.c

src/backend/access/transam/twophase.c

src/backend/access/transam/xlog.c

src/backend/commands/copy.c

src/backend/commands/define.c

src/backend/commands/functioncmds.c

src/backend/commands/sequence.c

src/backend/commands/tablecmds.c

src/backend/executor/execQual.c

src/backend/libpq/auth.c

src/backend/libpq/be-secure.c

src/backend/postmaster/bgwriter.c

src/backend/rewrite/rewriteHandler.c

src/backend/utils/adt/acl.c

src/backend/utils/adt/arrayfuncs.c

src/backend/utils/fmgr/dfmgr.c

...s/mb/conversion_procs/utf8_and_iso8859/utf8_and_iso8859.c

...end/utils/mb/conversion_procs/utf8_and_win/utf8_and_win.c

src/backend/utils/misc/guc.c