delta-find: split the "sparse" part of `_pre_filter_rev` in a method
Since `_pre_filter_rev` contains logic from various sources of constraint, we
start splitting is in subfunction to clarify and document the grouping.
[templates]
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}{branches}\n\n'
changeset_quiet = '\t* {desc|firstline|fill68|tabindent|strip}\n\n'
changeset_verbose = '{date|isodate} {author|person} <{author|email}> ({node|short}{tags}{branches})\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}]'
start_branches = ' <'
branch = '{branch}, '
last_branch = '{branch}>'
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* '