[krbdev.mit.edu #7187] ReST html docs render '--' as &#8211 (en dash)

[Benjamin Kaduk via RT]

We use '--' for the long form of command arguments in a few places in
the doc tree, most notably in krb_build/options2configure.rst .
When rendered into html (other formats are not checked and also
potentially problematic), the '--' becomes an en dash character,
represented in the html source as &#8211.
Since we are documenting the actual configure options, which use two
ASCII 055 characters (not a unicode en dash), we should have our
rendered documentation produce that output.

I forget whether it was Greg or Tom who pondered whether these arguments
should be in `` blocks anyway.
The sphinx/ReST documentation I've looked at so far does not make it
clear whether this conversion behavior is configurable.