contrib: have check-code look at files in latin1 instead of ascii
This way all files open. So far none of our patterns look like they'll care.
Differential Revision: https://phab.mercurial-scm.org/D4249
tests: port inline extension in test for beautifygraph to Python 3
test-glog-beautifygraph.t now passes on Python 3.
Differential Revision: https://phab.mercurial-scm.org/D4247