tests: fix regressions.

Exit status 63 is documented for version-mismatch.
	* bootstrap.conf (gnulib_modules): Remove sysexits.
	* src/system.h (EX_MISMATCH): Define.
	* src/parse-gram.y (version_check): Use it instead of EX_CONFIG.

Missing includes.
	* tests/calc.at, tests/named-refs.at: Include assert.h.

src/parse-gram.y

@@ -804,7 +804,7 @@ version_check (location const *loc, char const *version)
     {
       complain_at (*loc, "require bison %s, but have %s",
                    version, PACKAGE_VERSION);
-      exit (EX_CONFIG);
+      exit (EX_MISMATCH);
     }
 }