copies: refactor symmetricdifference as _findlimit
We only need to track the lowest revision seen, which makes things simpler.
header = '{date|shortdate} {author|person} <{author|email}>\n\n'
header_verbose = ''
changeset = '\t* {files|stringify|fill68|tabindent}{desc|fill68|tabindent|strip}\n\t[{node|short}]{tags}\n\n'
changeset_quiet = '\t* {desc|firstline|fill68|tabindent|strip}\n\n'
changeset_verbose = '{date|isodate} {author|person} <{author|email}> ({node|short}{tags})\n\n\t* {file_adds|stringify|fill68|tabindent}{file_dels|stringify|fill68|tabindent}{files|stringify|fill68|tabindent}{desc|fill68|tabindent|strip}\n\n'
start_tags = ' ['
tag = '{tag}, '
last_tag = '{tag}]'
file = '{file}, '
last_file = '{file}:\n\t'
file_add = '{file_add}, '
last_file_add = '{file_add}: new file.\n* '
file_del = '{file_del}, '
last_file_del = '{file_del}: deleted file.\n* '