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
header = header.tmpl
footer = ''
changeset = changeset.tmpl
difflineplus = '#line#'
difflineminus = '#line#'
difflineat = '#line#'
diffline = '#line#'
changesetparent = '# Parent #node#'
changesetchild = '# Child #node#'
filenodelink = ''
filerevision = '#rawfileheader##raw#'
fileline = '#line#'
diffblock = '#lines#'
filediff = filediff.tmpl
fileannotate = fileannotate.tmpl
annotateline = '#author#@#rev#: #line#'
manifest = manifest.tmpl
manifestdirentry = 'drwxr-xr-x {basename}\n'
manifestfileentry = '{permissions|permissions} {size} {basename}\n'
index = index.tmpl
indexentry = '#url#\n'