phabricator: convert unicode to binary when writing patches

This is a quick fix to make `hg phabread D189` work.

It seems we might want to replace all `r''` to `u''`, and add more
`encoding.*to*` to be more explicit when interacting with `json` module.

Differential Revision: https://phab.mercurial-scm.org/D192

contrib/phabricator.py

@@ -560,7 +560,8 b' def readpatch(repo, params, write, stack'
             if k in meta:
                 header += '# %s %s\n' % (_metanamemap[k], meta[k])
 
-        write(('%s%s\n%s') % (header, desc, body))
+        content = '%s%s\n%s' % (header, desc, body)
+        write(encoding.unitolocal(content))
 
 @command('phabread',
          [('', 'stack', False, _('read dependencies'))],