(bug 26204) font-size is too small

The Geshi rendered output has a font-size of 10px where we would expect
13px just like for <pre>.

Bug 33496 against MediaWiki core dealt with that issue already: in some
(all?) browser 'monospace' has a size of 13px where as the default is
16px. When defining a font-size of 0.8em the monospace is scaled down to
10 px which is too small. By appending another font statement, the
browser treat monospace as a default font and thus scale it starting
with 16px instead of 13px.

This patch append a style to geshi which set the font-family to
"monospace, monospace" thus tricking the browser in considering
monospace a regular font.

Change-Id: I7bbdcc0a21010513473a7ca9d784df77e9920b5b
Merge "(bug 26204) font-size is too small"