remove directory class from porters handbook

[jgh]

Summary

remove directory class from porters handbook

[wblock]

Some of these changes also mix in paragraph rewrapping (whitespace-only changes).

I'm not really sure if leaving the attribute out but leaving the tag broken over two lines works:
<filename

/usr/local</filename>

If that works, then combining those lines should be done in a separate whitespace-only edit.

[wblock]

Good. Please build-test before commit. A followup whitespace-only cleanup would be nice, but is not required.