pawgo: correctly pass dir/base object names to hist mgr
pawgo's histogram manager used to completely split a requested histogram name by '/' tokens, after having first extracted the file id header.
This wasn't taking into account histograms that were directory namespaced, e.g.:
paw> /hist/open hh /file/id/ff/my/histo
was trying to request the histogram "my" instead of "my/histo" from the rio file.
This CL addresses this.
Fixes #120 (closed).