[MRG] hist: fix new_binning_template, properly set bins of copied axes

![binmerge2d](https://f.cloud.github.com/assets/202816/1187441/5b6f1c2e-2379-11e3-8a8b-0cb28c1e97fa.gif)

This PR fixes a bug where the bin edges of the unmodified axes in new_binning_template were not set correctly.