Item11476: accelerate RcsLite for large numbers of revisions. There is still a fundamental problem with the way RCS organises the file that makes fast reading difficult, but the changes here will at least accelerate those operations that only require a subset of the history.

git-svn-id: http://svn.foswiki.org/trunk/core@16645 0b4bb1d4-4e5a-0410-9cc4-b2b747904278