templates: adjust white space amount in the output of {whyunstable}
There used to be 2 spaces between divergent nodes (when not using custom
template for divergentnodes) because divergentnodes is a hybrid list, which
means it gets ' '.join()ed, but formatnode() already had a space. Now it
doesn't, which requires extra effort in writing custom templates for
whyunstable, but at least it looks correctly by default.
Test output needs to be sorted for stability.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.