Specify a last modification date in copyright headers

Writing in a license header "Copyright 2004-present" doesn't actually make the copyright term extend to whenever someone happens to read it. This kind of wishful thinking surely invalidates whatever protective effect the header may have provided.

This pull request has three commits: the first updates license.php to include the actual current year, the second is the result of running the new license.php, and the third updates some license headers missed by license.php.