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.
warning
error
'buffered\n'
colored? True
colored? True