tests/test-check-code.t

cmdutil: pass node instead of ctx to diffordiffstat

93bcc73df8d5 changed showpatch to use ctx's more, but it accidentally passed
prev as a context and node as a binary string, when both should be passed as
binary strings (since diffordiffstat tries to resolve them via repo[X]).

This affected hggit since the existing ctx belongs to the git overlay, but the
resolved context (from the repo[X] resolution) should belong to the main repo.
This broke a test because it tried to look in the git repo for data that didn't
exist.

This feels like a deeper issue in hggit somewhere, but the fix is here trivial and
obviously more correct

#require test-repo

  $ check_code="$TESTDIR"/../contrib/check-code.py
  $ cd "$TESTDIR"/..

New errors are not allowed. Warnings are strongly discouraged.
(The writing "no-che?k-code" is for not skipping this file when checking.)

  $ hg locate | sed 's-\\-/-g' |
  >   xargs "$check_code" --warnings --per-file=0 || false
  Skipping hgext/zeroconf/Zeroconf.py it has no-che?k-code (glob)
  Skipping i18n/polib.py it has no-che?k-code (glob)
  Skipping mercurial/httpclient/__init__.py it has no-che?k-code (glob)
  Skipping mercurial/httpclient/_readers.py it has no-che?k-code (glob)
  Skipping mercurial/httpclient/socketutil.py it has no-che?k-code (glob)