Thanks to stephaneyfx from the #rust IRC channel for showing me that
this needs separate type parameters on the functions in order to
compile.
The only API change that can't be helped are the `line_junk` and
`char_junk` function pointers in the Differ struct, which now take
`&&str` and `&char` parameters, respectively. This is probably for the
better, since `char_junk` now operates on Unicode scalar values rather
than the single UTF-8 bytes disguised as `&str` that were previously
retrieved via the unsafe `slice_unchecked()` function.
David Stern