hgweb.cgi and hgwebdir.cgi fixes/cleanups for user configurable parts: - "import os" was missing in hgwebdir.cgi, added to comments for both script. - HGENCODING has to be set before importing hgweb, otherwise you'll get mixed encoding in changelog vs. file content/diffs. - "import sys" is only needed when changing sys.path - document purpose of cgitb.