subrepo: rename the '_ui' member to 'ui'
The localrepository class has a 'ui' member, so keeping the names the same will
allow for duck typing with subrepo instances when accessing 'ui'. Changing this
is easier than finding all of the localrepository instance uses and renaming
that to '_ui'.
Test update logic when there are renames
Update with local changes across a file rename
$ hg init
$ echo a > a
$ hg add a
$ hg ci -m a
$ hg mv a b
$ hg ci -m rename
$ echo b > b
$ hg ci -m change
$ hg up -q 0
$ echo c > a
$ hg up
merging a and b to b
warning: conflicts during merge.
merging b incomplete! (edit conflicts, then use 'hg resolve --mark')
0 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
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