[metapost] verbatimtex not used from an .mp include file?

[Sanjoy Mahajan]

Oh well.  Where is it documented?  p.21 of the MetaPost User's manual
discusses verbatimtex but doesn't mention that restriction.

-Sanjoy

`Never underestimate the evil of which men of power are capable.'
         --Bertrand Russell, _War Crimes in Vietnam_, chapter 1.