FACTOR: Mark translatable string as not a printf format string.

FACTOR: Mark translatable string as not a printf format string.

gettext uses a heuristic to guess whether a translatable string is a printf
format string.  In this case, it guesses wrong, so add a comment that tells
gettext that "% of Variance" is not a format string.

Without this change, the translationproject.org robot rejects translations.

Reported by fxmiguel@gmail.com.