parse_declaration(): be more lenient in what we accept. We now

parse_declaration(): be more lenient in what we accept.  We now
basically accept <!...> where the dots can be single- or double-quoted
strings or any other character except >.

Background: I found a real-life example that failed to parse with
the old assumption: http://www.opensource.org/licenses/jabberpl.html
contains a few constructs of the form <![if !supportLists]>...<![endif]>.