Address 'make sc_error_message_uppercase' failures.

Address 'make sc_error_message_uppercase' failures.

* m4/output.c (m4_freeze_diversions): Silence false positive.
* src/main.c (main): Use 'warning', not 'Warning', in messages.
* m4/utility.c (m4_verror_at_line): Likewise.
* doc/m4.texinfo (Operation modes, Macro Arguments, Undefine)
(Defn, Pushdef, Indir, Builtin, Ifdef, Ifelse, Dumpdef, Trace)
(Debuglen, Debugfile, Dnl, Changeresyntax, Standard Modules)
(Index macro, Regexp, Substr, Translit, Patsubst, Format, Incr)
(Eval, Mkstemp, Syncoutput, Improved forloop)
(Improved fatal_error): Adjust expected output.
* tests/builtins.at (define, mkdtemp, mkstemp): Likewise.
* tests/freeze.at (loading format 1, reloading unknown builtin):
Likewise.
* tests/macros.at (Arity and defn, 'Arity, defn, and freeze')
(pushdef/popdef): Likewise.
* tests/null.err: Likewise.
* tests/options.at (deprecated options, POSIXLY_CORRECT)
(--fatal-warnings, --regexp-syntax, --syncoutput): Likewise.
* tests/others.at (nul character, stdin seekable): Likewise.
* tests/modules.at (AT_CHECK_M4_MODTEST, modules: text):
Likewise.

Signed-off-by: Eric Blake <ebb9@byu.net>