MINOR: stats: don't use a monospace font to report numbers

On several browsers, the monospace font used to display numbers in tips
is not much readable. Since the numbers are aligned anyway, there is too
little benefit in using such a font.
MINOR: session: remove debugging code

The memset() was put here to corrupt memory for a debugging test,
it's not needed anymore and was unfortunately committed. It does
not harm anyway, it probably just slightly affects performance.