revlog: reduce memory usage in addgroup
- use a buffer to extract the delta from a chunk
- avoid concatenating to a compressed delta
- use a buffer to directly extra full text from a trivial delta
- delete chunk and delta objects after use
changeset = '{rev}{tags}{parents} {node|short} {date|isodate} {author|user}\n {desc|firstline|strip}\n\n'
changeset_quiet = '{rev}:{node|short}\n'
start_tags = '['
tag = '{tag},'
last_tag = '{tag}]'
start_parents = ':'
parent = '{rev},'
last_parent = '{rev}'