clip relative to widget popups to window
change center position based on scroll position
fire close handler when popup is hidden
fix popup close handler
make center popup positioner more extendable
simplify popup positioners
add closehandler test
remove duplicate method
simplify and remove duplicate code
single return from method
simplify with double return
simplify canFitOnRightEdge
fix javadoc
Merge pull request #600 from rdwallis/relpop

clip relative to widget popups to window