rhg: Rename some revlog-related types and methods
Use "data chunck" and "data" for a revlog entry’s data before and after
resolving deltas (if any), repsectively.
The former `FilelogEntry` actually only contains data, rename it to
`FilelogRevisionData` accordingly. This leaves room to later have a
`FilelogEntry` type that wraps `RevlogEntry`.
Differential Revision: https://phab.mercurial-scm.org/D11959
#require serve
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[100]
$ test -d copy
[1]
$ "$PYTHON" "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[100]
$ killdaemons.py