Fix hgweb.filediff
The third argument to hgweb.diff should be a list, not a string.
This fixes a bug found by xorAxAx, where hgweb would also show the diff
for "README" when you ask for the diff for "Demo/cgi/README".
changeset = 'changeset: {rev}:{node|short}\n{tags}{short_parents}user: {author}\ndate: {date|date}\nsummary: {desc|firstline}\n\n'
changeset_quiet = '{rev}:{node|short}\n'
changeset_verbose = 'changeset: {rev}:{node}\n{tags}{parents}{manifest}user: {author}\ndate: {date|date}\nfiles: {files}\n{file_adds}{file_dels}description:\n{desc|strip}\n\n\n'
start_file_adds = 'files+: '
file_add = ' {file_add}'
end_file_adds = '\n'
start_file_dels = 'files-: '
file_del = ' {file_del}'
end_file_dels = '\n'
short_parent = 'parent: {rev}:{node|short}\n'
parent = 'parent: {rev}:{node}\n'
manifest = 'manifest: {rev}:{node}\n'
tag = 'tag: {tag}\n'