Rename automake_tests to check_automake_vulnerabilities and simplify

Rename automake_tests to check_automake_vulnerabilities and simplify

This also moves the checks for known GNU Automake CVE issues to the
top-level, and eliminates the now-otherwise-useless check_vulnerabilities
and check_files procedures.  The major impetus for this simplification
of the call graph was the observation that check_vulnerabilities, while
named generically, was associated with a log message citing specifically
CVE-2009-4029 and CVE-2012-3386, combined with noticing that all other
functionality had been factored out of check_files.