[PATCH] StatHist refactoring interim merge, proposed fix for bug 3381

Hi all,
   here's a new interim merge proposal for the StatHist refactoring
effort. This merge aims to close bug 3381 and advance a bit the
general StatHist refactoring effort.

What it does:
- change the type used for StatHist counters to uint64_t (parametric
as StatHist::bins_type)
- change the index for StatHist bins to unsigned
- bring stub_StatHist forward and actually use it, also to remove some
objects from tests

What crept in:
- an initial effort for a StatHist unit test.
- some src/Makefile.am cleanup

-- 
    /kinkie