Use reference substitutions for paths in docs

Use reference substitutions for paths in docs

For the default doc build (used for the web site and release tarball),
substitute path variables with links to the paths table in
mitK5defaults.rst, using symbolic names for the link text.

The substitution of kdcdir for man pages is slightly altered as a
side-effect of this commit.  Regenerate the man pages to match.  The
rendered man pages are unchanged.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25794 dc483132-0cff-0310-8789-dd5450dbe970