vfs: make it possible to pass multiple path elements to join os.path.join(), localrepo.join() and localrepo.wjoin() allow passing multiple path elements; vfs.join() should be as convenient.

largefiles: drop os.path reference in lfutil.storepath() localrepo.join() can concatenate multiple parts on its own.

histedit: fix preventing strips during histedit We were trying to prevent strips of important nodes during histedit, but the check was actually comparing the short hashes in the rules to the exact value the user typed in, so it only ever worked if the user typed a 12 character hash.

copies: pass changectx instead of manifest to _computenonoverlap The _computenonoverlap function takes two manifests to allow extensions to hook in and read the manifest nodes produced by the function. The remotefilelog extension actually needs the entire changectx instead (which includes the manifest) so it can prefetch the subset of files necessary for a sparse checkout (and the sparse checkout depends on which commit is being accessed, hence the need for the changectx). I have tests in the remotefilelog extension that cover this.