makefile: don't use system hgrc when running hg in-place
This suppresses the printing of spurious error messages if a global
hgrc refers to extensions that the in-place hg can't access.
setup: print subprocess stderr if there is any
I just spent 1.5 days trying to debug a failing buildbot because
setup.py was silently dropping the errors that were being printed
by in-place hg.