[Bioc-devel] Gviz AlignmentTrack ylim patch

First, let me say thanks for such an excellent genome visualization 
package.  I simply couldn't find anything comparable when it came to 
producing publication quality genome plots.

I've run what seems like a bug to me, and I've attempted to provide a 
suitable patch.  The bug is in the coverage portion of an 
AnnotationTrack.  It seems that if one supplies a `ylim` value, the 
printed scale will be adjusted as requested, but the graph will still 
be plotted in the automatically determined scale.

Example plotting graphs without setting ylim (not the scales for each 
are different): http://i.imgur.com/68xObgx.png
Example of graphs with ylim set (but not properly honored): 
http://i.imgur.com/MBvO2wA.png
Example of patched code with ylim set (now the ylim is used properly): 
http://i.imgur.com/EXlrkqa.png

I hope this helps to resolve what I think is an unintended bug.