return bbox immediately to save several CPU cycles
bugfix: intersected geom should be initiated with a fresh copy of self
cleanup: remove unnecessary debug info
bugfix: calculate page zoom before hinting
add scroll mode for pdf/djvu reader
bugfix: reset page scroll states when switching reflow on/off
bugfix: recalculate screen offset
Merge pull request #781 from chrox/pdf_scroll_mode

add scroll mode for pdf/djvu reader