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.
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors