#18 PageUp and PageDown keys don't flip pages

[Brak]

When using pageup/pagedown to scroll through a book,
the viewer will not load the next or previous page once
the top or bottom of the current page has been reached.

Example, when reading an encylopedia article it's
useful not to have to go back to the mouse to reach the
next page.

-Joerg

[Dr Bill C Riemers]

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This is modeled off the LT viewer and DjVuLibre viewers.
Space and Backspace flip pages. Page up and Page down
scroll the pages.