tick label, histogram, errorbar, and legend

I have a few comments which may help to improve the matplotlib functionality:

(1) When the data values are large (or small), the mantissas are rounded off
    in the scientific notation of the x- or y-tick labels. For example:


In fact, this is a generally harder problem. In the following contrived and
unlikely situation, it shows the similar problem:


This example has another curious problem. The tick labels are overploted in
some places and missing in others.

(2) Right now, hist() can only plot filled "bar charts". It will be
nice if it can also plot not-filled bar charts, bars without gaps in between,
filled with color of choice, and histogram with only the top bar, without
the vertical bars, except at the ends.

(3) For asymmetric error bars, the x(y)err's first array is for the "-" and
the second for the "+". Will it be more intuitive to have that reversed?

(4) When symbols are plotted (e.g. "o" or "x"), the legend shows a bunch (4)
of them. Will it be better to just plot one?


JC Hsu