Update ggplot-heatmap.R so that column names follow the dendrogram/heatmap

Previously, the column names (leaves on the dendrogram) were not plotted with their respective branches created by hierarchical clustering. Instead, they were displayed in their original input order.

I changed labels=colnames(x) to labels=colnames(xx) in col.plot in ggheatmap function and the order of "##order of dendros" wrt "##dendro plots".

![ggheatmap_ex](https://f.cloud.github.com/assets/5115662/1676539/3eaa15ea-5d1b-11e3-8280-8299a15cc2a4.png)

Thank you for sharing this script, it was very helpful!