Move location attribute into ValidationError
Move location attribute into ValidationError

In concept every validation error should have the potential to provide
information on where in an XML document the problem was detected.  Define
the attribute at the root of the hierarchy so that user handlers can
reference it.

jonfoster/pyxb-upstream-mirror,jonfoster/pyxb-upstream-mirror,jonfoster/pyxb2,jonfoster/pyxb2,balanced/PyXB,CantemoInternal/pyxb,CantemoInternal/pyxb,pabigot/pyxb,CantemoInternal/pyxb,jonfoster/pyxb2,jonfoster/pyxb-upstream-mirror,balanced/PyXB,balanced/PyXB,pabigot/pyxb