wiki/LICENSE.TXT: added message about including _license/ when redistributing, as for /LICENSE.TXT
wiki/_license/LICENSE.TXT: replaced with README.TXT as in /_license
wiki/LICENSE.TXT: changed "the page text of the wiki" to "the wiki's components" since some of the attachments will eventually be marked as open-source
added wiki/LICENSE.TXT,_license/, with license terms that apply specifically to the wiki (which is BSD, not GPL). note that the wiki attachments are NOT open-source, only the page text.