changegroup: add "vfs" argument to "writebundle()" for relative access via vfs Before this patch, filename specified to "changegroup.writebundle()" should be absolute one. In some cases, they should be relative to repository root, store and so on (backup before strip, for example). This patch adds "vfs" argument to "writebundle()", and makes "writebundle()" open (and unlink) "filename" via vfs for relative access, if both filename and vfs are specified.