Reduce string duplication in compression code This cuts down on string copies and allows buffers (instead of strings) to be passed into the compression code

reset mtime when two files are equal

add localrepo.wlock for protecting the dirstate - add localrepo.wlock - nest it in localrepo.lock - protect the code that change the dirstate

add a releasefn keyword to lock.lock releasefn is a function that will be executed when the lock is released