assertEqual returns False when comparing two arrays with different shapes

instead of raising a ValueError due to failed broadcasting
convert 0d arrays returned by numexpr to scalars

numexpr returns 0d arrays when given scalars
trunc needed to be updated too
removed useless shows in test
reenable charts tests that I disabled by mistake
added test for the "groupby(expr1, expr=count(expr2) / count()) used in an expr" issue