Remove use of non ASCII characters in literals.

We would prefer that we don't use non ASCII characters in either string
or character literals.  In theory, every editor and tool would ensure
that these characters are not translated to some random encoding or
otherwise become corrupted.  In practice, we're just going to err on the
side of caution.
Replace non ASCII characters in comments with ASCII equivalents.
Merge branch 'remove-unicode-characters'