scripts: Add commit-msg check for patch references
    
    References in the commit message are important when generating the RPM
    changelog.
    Although scripts/log takes into account References: header, a reference
    may possibly be missed out when the script is skipped or the message
    misedited.
    
    Add a new hook that validates that the commit message contains all newly
    added references.
    
    Signed-off-by: Michal Koutný <mkoutny@suse.com>