i18n: fix "% inside _()" problems
Before this patch, "contrib/check-code.py" can't detect these
problems, because the regexp pattern to detect "% inside _()" doesn't
suppose the case that the format string and "%" aren't placed in the
same line.
This patch replaces "\s" in that regexp pattern with "[ \t\n]" to
detect "% inside _()" problems in such case.
"[\s\n]" can't be used in this purpose, because "\s" is automatically
replaced with "[ \t]" by "_preparepats()" and "\s" in "[]" causes
nested "[]" unexpectedly.
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