templater: consistently join() string-like object per character (BC)
The old behavior was copied from join() of a lazy generator string, which
was unified to the behavior of join() of a byte string by the previous patch.
This patch fixes the mappable type to do the same.
#require docutils gettext
Error: the current ro localization has some rst defects exposed by
moving pager to core. These two warnings about references are expected
until the localization is corrected.
$ $TESTDIR/check-gendoc ro
checking for parse errors
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.