Additional appendfile fixes for interleaved data/index files
The appendfile code was not passing default version info to the
changelog or manifest classes, and so they were always being created
as version 0.
revlog.checkinlinesize had to be corrected to seek to the end
of the index file when no index file was passed (only clone does this)
Speedup revlog.ancestors for the linear case
revlog.ancestors can be expensive on big repos. This cuts down the overall
time for hg update by ~19% by short cutting revlog.ancestors when one of the
revisions is reachable from another.