properties.py's Interpolate()'s config.error messages needs to point out where the issue is

I was migrating off 0.8.4 to 1.2.0 and was changing WithProperties() to util.Interpolate().

However, there was a long list of config.errors, most of which were repeated:

invalid Interpolate default type 'b'

Could not quite figure out where the issue lay, so I went and modified the following line:
(buildbot/process/properties.py:763)

config.error("invalid Interpolate default type '%s' from %s : fmtstring = %s" % (repl[0], repl, fmtstring)

That's when I realized I had missed some "%(prop:prop:basedir)s changes as well as some %(basedir)s
changes to %(prop:basedir)s (unreleated).

Is it possible to show the line# and file name from where this error comes from? This also applies
to the 'invalid Interpolate selector '%s'".. and others.