* acgeneral.m4 (AC_CANONICAL_THING): define, not AC_DEFUN.
Don't AC_PROVIDE, there is no need.
When calling `config.sub`, also || exit 1, to catch failures from
config.sub.
* acspecific.m4 (AC_SYS_LONG_FILE_NAMES): Use ac_val, not val.
(AC_EXEEXT): Use ac_file, not file.
* tests/actest.m4: New file, holding extra Autoconf macros used
during the testing.
(AC_ENV_SAVE): New macro, save the sh variables in a file.
* tests/suite.m4 (AT_TEST_MACRO, Generation of configure.in):
include actest.m4, and call twice AC_ENV_SAVE to compare the
variables before and after the macro.
* tests/Makefile.am (macro.m4): Don't test macros that are
required: they will be tested somewhere else.
