stddoclet: Combine near-duplicate methods for getting package path: getPackagePath, getDirectoryPath

I notice we have a method SourceToHTMLConverter called getPackagePath that is
nearly identical in function to one DirectoryManager called getDirectoryPath.
It looks like the first method always ends in a slash while the other
doesn't. They could still be reduced to a single method.

I'd favor the first implementation, which has fewer lines, uses methods
designed specifically for this task, and it has a better
name. It should be using StringBuffer rather than String,
and should be located in DirectoryManager.

We need to decide whether the method should keep the trailing slash or not.

    /**
     * Get the package path
     * @param pd the package to get the path for.
     * @return a path for the package
     */
    public static String getPackagePath(PackageDoc pd) {
        if (pd == null) {
            return "";
        }
        StringTokenizer st = new StringTokenizer(pd.name(), ".");
        String result = "";
        while (st.hasMoreTokens()) {
            result += st.nextToken() + File.separator;
        }
        return result;
    }


     public static String getDirectoryPath(PackageDoc pd) {
        if (pd == null) {
            return "";
        }
        String name = pd.name();
        StringBuffer pathstr = new StringBuffer();
        for (int i = 0; i < name.length(); i++) {
            char ch = name.charAt(i);
            if (ch == '.') {
                pathstr.append(fileseparator);
            } else {
                pathstr.append(ch);
            }
        }
        return pathstr.toString();
    }