Fixes for check_apt handling of -i/-e/-c regexps and SECURITY_RE, plus tests

 * Fix for Debian bug #522812 (check_apt -c broken)
 * Fix for bug 1904965 from Nagios SourceForge tracker (check_apt: SECURITY_RE is not correct)
 * Add hidden `--input-file` option to check_apt, allowing it to take sample apt output as input (modelled on check_procs)
 * Test script for check_apt with test cases for my fixes above (modelled on `tests/check_procs.t`)