largefiles: headers and values need to be sysstrs, add r prefixes

# skip-blame just some r prefixes

Differential Revision: https://phab.mercurial-scm.org/D2606

hgext/largefiles/proto.py

@@ -97,7 +97,7 b' def wirereposetup(ui, repo):'
             # it ...
             if issubclass(self.__class__, httppeer.httppeer):
                 res = self._call('putlfile', data=fd, sha=sha,
-                    headers={'content-type':'application/mercurial-0.1'})
+                    headers={r'content-type': r'application/mercurial-0.1'})
                 try:
                     d, output = res.split('\n', 1)
                     for l in output.splitlines(True):