addbackup: handle file in subdirectory
The current naming scheme ('journal.backups.<file>') resulted is bad directory
name when 'file' was in a subdirectory. We now extract the directory name and
create the backupfile within it.
We plan to use file in a subdirectory for cachefile.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a