Move RELEASE-NOTES changelog stuff from r18961 and r18993 to the MediaWiki 1.10 HISTO...

Move RELEASE-NOTES changelog stuff from r18961 and r18993 to the MediaWiki 1.10 HISTORY file ... Since I've done the same thing previously (accidentally threw away the changelog after 1.8 was released), seems only right that I put it back :-)

I don't know whether the HISTORY file should include all the detailed "Compatibility changes" / "Behavior changes" / "Database change" / "Configuration changes" stuff, or just the more compact list of changes with bug numbers - so I have included everything, since it should hopefully be easy to delete stuff if there is too much detail.