Implemented fix to issue 196 on github for log=True and histtype='step'
fixed the minimum specification in ax.hist as per @WeatherGod's comment;
only want to set min this way if log is specified.  Also, added case for
normed vs not
Use numpy.min
Add hist step log test
Use actual log base, instead of assuming a default
Upate comments in hist to be more descriptive
Merge pull request #1684 from dmcdougall/fix_loghist

Fix hist for log=True and histtype='step'