standardize some error messages

standardize some error messages

* maint.mk: (sc_error_message_warn_fatal, sc_error_message_uppercase):
(sc_error_message_period): Add automatic checks for non-standard error
messages.
* .x-sc_error_message_uppercase: explicit exclusion for this check
* src/cp.c: Standardize some error messages.
* src/date.c: Likewise.
* src/dircolors.c: Likewise.
* src/du.c: Likewise.
* src/expr.c: Likewise.
* src/install.c: Likewise.
* src/join.c: Likewise.
* src/ln.c: Likewise.
* src/mv.c: Likewise.
* src/od.c: Likewise.
* src/pr.c: Likewise.
* src/split.c: Likewise.
* src/truncate.c: Likewise.
* src/wc.c: Likewise.
* tests/du/files0-from: Expect new error message.
* tests/misc/join: Likewise.
* tests/misc/split-a: Likewise.
* tests/misc/wc-files0-from: Likewise.
* tests/misc/xstrtol: Likewise.
* lib/xmemxfrm.c: Likewise.