Summary: Update import statements and code to match core linters.
Test Plan:
`run-tests.py -j8`
Source these versions of phabdiff.py, arcdiff.py, and phabstatus.py in my hgrc. Run hg st, diff, ssl and observe no crashes.
Reviewers: durham, rmcelroy, phillco, #mercurial
Reviewed By: rmcelroy
Subscribers: rmcelroy, quark, awestern
Differential Revision: https://phabricator.intern.facebook.com/D6680961
Signature: 6680961:1515578477:ea5f1591e390f6ca8a94f652daeb1db9de819fea
