setup: use sysstr() on process output
Otherwise we get a str-bytes mismatch on Python 3 if
an error occurs.
Differential Revision: https://phab.mercurial-scm.org/D8469
# name space package to host third party extensionsfrom__future__importabsolute_importimportpkgutil__path__=pkgutil.extend_path(__path__,__name__)