small changes to b_and_w_plotting

polycollections and pathcollections are now treated seperately. In case
of polycollections you can control whether you want to use hatching or
greyscaling. This style is reflecting in the figure legend as well.
changes in prim

new option in prim to drop one or more uncertainties from the
experiment array.
some bug fixes needed due to changes in numpy 1.7
some additional test code to test these changes