fix appendfile problem on macos.
when i open file with mode 'a+' on linux, seek position is 0.
on macos seek position is end of file instead. not documented.
header = header-raw.tmpl
footer = ''
changeset = changeset-raw.tmpl
difflineplus = '#line#'
difflineminus = '#line#'
difflineat = '#line#'
diffline = '#line#'
changesetparent = '# parent: #node#'
changesetchild = '# child: #node#'
filenodelink = ''
filerevision = filerevision-raw.tmpl
fileline = '#line#'
diffblock = '#lines#'
filediff = filediff-raw.tmpl
fileannotate = fileannotate-raw.tmpl
annotateline = '#author#@#rev#: #line#'