(AC_PREFIX_PROGRAM): Use macros of the AC_TR_ family.

(AC_PREFIX_PROGRAM): Use macros of the AC_TR_ family.
(AC_HAVE_LIBRARY): Likewise.
(AC_CHECK_FUNCS): Likewise.
(AC_CHECK_FILES): Likewise.
(AC_CHECK_SIZEOF): Likewise.
(AC_TR): New macro which performs transliteration by m4 when possible,
or by `tr' at configure time.
(AC_TR_UPCASE_NAME): New macro, transliteration 'a-z' to 'A-Z'.
(AC_TR_UPCASE_FILE): New macro, transliteration 'a-z./-' to 'A-Z___'.
(AC_TR_SH): New macro, transliteration to valid sh var name.
(_AC_SH_QUOTE): New macro which protects non protected backquotes
against shell expansion.
(AC_MSG_CHECKING): Use it.
(AC_CHECKING): Use it.
(AC_MSG_RESULT): Use it.
(AC_VERBOSE): Use it.
(AC_MSG_WARN): Use it.
(AC_MSG_ERROR): Use it.
(_AC_MESSAGE): New macro to report message at m4 time.
(AC_WARNING): New macro to report warnings at m4 runtime.
(AC_FATAL): New macro, to report fatal error at m4 runtime.
(AC_VAR_IF_INDIR): New macro.
(AC_VAR_SET): Likewise.
(AC_VAR_GET): Likewise.