png( "commits_month.png", width = 1000, height= 700 ) 
print( xyplot( commits ~ date , data = monthdata, ylab = "commits / month",
    panel = function(x, y, ...){
        panel.yearlines() 
        panel.abline( h = pretty(y), lwd = .5, col = "gray" )
        panel.loess.fill( x, y, start = as.Date("1997-01-01"), 
            end = as.Date( "2010-01-01" ), by = "month", 
            lwd = 2, col = "black", ... )
        panel.xyplot( x, y, pch = "+", ... )
    }, axis = axis.releases ) )
dev.off()