localrepo/branchcache: kill unused localrepo.branchcache
The UTF-8 version of the branchcache is the master, always up-to-date, we can
rename it to localrepo._branchcache.
#!/bin/sh
hg init repo
cd repo
touch foo
hg ci -Am 'add foo'
hg up -C null
# this should be stored as a delta against rev 0
echo foo bar baz > foo
hg ci -Am 'add foo again'
hg debugindex .hg/store/data/foo.i