Skip over 'fragments' directory when scanning for PODs

Skip over 'fragments' directory when scanning for PODs

The generate-html script scans the directories to compile a list of
POD files.  The list of candidates include the 'fragments' directory,
which causes an error when the script attempts to open it as a file.

Change-Id: If1208561f58f869ccba60f4a263bee5200dad1ed
Reviewed-on: http://gerrit.openafs.org/2494
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Russ Allbery <rra@stanford.edu>
Tested-by: Russ Allbery <rra@stanford.edu>