templater: deduplicate iterator of overlay mappings

templater: complain about invalid application of '%' operator (BC) Before, '{x % y % z ...}' was silently evaluated as '{x % y}'. We no longer need this hack since the web template bugs was fixed by earlier patches. At this point, the error message may contain '<generator *>', which will be fixed later.

hgweb: fix type of {nav} keyword when linerange filter is active Spotted by making '%' operator check the operand type more strictly. Before, "{nav}" would be evaluated to a lazy "" (empty string) and {"" % x} would yield one empty string.

hgweb: fix {diff} expansion in JSON template The same sort of bug as the previous patch. In this case, I decided to fix the JSON template since we aren't ready to fix the {diff} keyword without BC. I'll rework it later.

hgweb: fix summary {tags} and {shortlog} to not forcibly expand template The same sort of bug as the previous patch. In this case, JSON template was wrong.

hgweb: fix search {entries} to not return results of template expansion "{entries%changelogentry}" in raw/search.tmpl was utterly wrong because "{entries}" here was a generator yielding results of template expansion. That's why we have a weird hack in runmap(), which I'm going to get rid of. https://www.mercurial-scm.org/repo/hg/file/4.5.2/mercurial/templater.py#l469 We have two choices: a) drop "%changelogentry" from raw/search.tmpl b) fix "{entries}" to yield mappings I take (b) because that's what the other log-like "{entries}" do. The "entries" keyword is wrapped by mappinggenerator so "{entries}" without "%searchentry" still works.