st: easy histogram

[David Airey <david.airey@Vanderbilt.Edu>]

I'm curious why there is an xscale(log) option in the easy histogram 
dialog. When I do:

clear
sysuse auto
histogram mpg, saving(h1, replace)
histogram mpg, xscale(log) saving(h2, replace)
gen logmpg = log(mpg)
histogram logmpg, saving(h3, replace)
graph combine h1.gph h2.gph h3.gph

I get what I expect in the first and third histogram commands, but not 
the second. The bars are stretched widthwise in the second histogram, 
such that I don't think the density adds to 1. In some twoway commands, 
changing the xscale to log when you have estimated a model on x and not 
log(x) is an incorrect procedure. Is this another instance? If so, I 
think it should be disallowed. Easy graph dialogs should be easy.

-Dave

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