Do not test internal methods.

Remove workarounds added while implementing --wrap, so that redundand
trailing sequences like `\x1b[32m\x1b[0m` are removed.

Also, actually run wrap regression tests; it should have been done in
the --wrap commit but somehow slipped away while addressing PR comments.

Which causes long lines to be nicely wrapped in side-by-side mode. To be
used primarily with `-s -w0`.

Excludes E203 whitespace before ':' for now.

TODO: look into pep8 for why `# nopep8` does not work here

This is useful for avoiding crashing on "cdiff -l" (on Python 3) in
https://github.com/myint/cppclean.

Also handle unknown encodings gracefully rather than crashing.

If need to support normal diff, writing a ndiff to udiff translator
makes more sense