(bug 17602) fix Monobook action tabs not quite touching the page body

(bug 17602) fix Monobook action tabs not quite touching the page body

This was caused by insufficient bottom padding on the tabs (0.1em on
normal ones, and for some reason 0.2em on active ones, which was
apparently enough). In some browsers (at least Opera) this resulted in
a one-pixel gap between the tabs and the page body.

This patch raises the padding to 1em, just in case. This shouldn't
cause any issues, as all z-indices are set reasonably on the involved
elements; the excess space is hidden "under" the page body.

Change-Id: I07223ba46913f721907f9aa88f79bc94402b6cf6