Check that the AC_DEFINEs from acspecific.m4 do have a template.

Check that the AC_DEFINEs from acspecific.m4 do have a template.
Fix the discovered bugs.

* tests/atgeneral.m4 (AT_CHECK): Don't just exit 1 when you want
to propagate the failure of a test: exit with the same exit
status, at least to preserve 77 (=ignore).
* tests/syntax.m4 (TEST_MACRO): Run also autoheader.  Don't run
this test on all the macros, some just cannot run without
arguments.
* acgeneral.m4 (AC_OUTPUT_CONFIG_STATUS): In the if egrep/fi for
#define templates, add a `:' to prevent syntax errors in
config.status when there are no AC_DEFINE performed.
* autoheader.m4 (AH_TEMPLATE): Don't use _AC_SH_QUOTE here, use it
in...
(AH_VERBATIM): here.  Now AH_C_UNSIGNED_CHAR is no longer failing
(formerly it would produce a non backslashed backquote, which
made sh choke).