Bug fix: scroll_page_count ".33" syntax should be "/.33".

The irssi docs state:
".33 = Scroll about a third of a page."
but ".33" value scroll about 3 lines actually. Further ".99" scrolls
about one line.
There is obviously typo in docs and it should have been:
"/.33 = Scroll about a third of a page."

Thats what we fix here.