check-code: add rule to detect usage of external diff via extdiff
This rule detects "hg extdiff" invocation without -p/--program and
-o/--option.
This patch specifies "-p diff" explicitly in test-extdiff.t to avoid
false positive matching.
changeset = '{rev}{tags}{bookmarks}{parents} {node|short} {date|isodate} {author|user}\n {desc|firstline|strip}\n\n'
changeset_quiet = '{rev}:{node|short}\n'
changeset_verbose = '{rev}{tags}{parents} {node|short} {date|isodate} {author}\n {desc|strip}\n\n'
start_tags = '['
tag = '{tag},'
last_tag = '{tag}]'
start_parents = ':'
parent = '{rev},'
last_parent = '{rev}'
start_bookmarks = '['
bookmark = '{bookmark},'
last_bookmark = '{bookmark}]'