largefiles: put whole "hgupdaterepo" process into the same "wlock" scope
Before this patch, there are two distinct "wlock" scopes below in
"hgupdaterepo":
1. "merge.update" via original "hg.updaterepo" function
2. "updatelfiles" specific "wlock" scope (to synchronize largefile
dirstate)
In addition to them, "dirstate.walk" is executed between these "wlock"
scopes.
But these should be executed in the same "wlock" scope for
consistency, because many (indirect) users of "hg.updaterepo" don't
get "wlock" explicitly before invocation of it.
"hg.clean" is invoked without "wlock" from:
- mqrepo.restore in mq
- bisect in commands
- update in commands
"hg.update" is invoked without "wlock" from:
- clone in mq
- pullrebase in rebase
- postincoming in commands (used in "hg pull -u", "hg unbundle")
- update in commands
This patch puts almost all original "hgupdaterepo" implementation into
"_hgupdaterepo" to reduce changes.