Genera's FS:DIRECTORY-LIST signals errors

[Gary Palter]

ASDF uses FS:DIRECTORY-LIST on Genera to enumerate the contents of the source repositories. However, if the directory doesn't exist, FS:DIRECTORY-LIST signals an error. ASDF expects to get NIL in this case instead. Here's a diff of a fix.

--- asdf.lisp.~1~ 2015-11-17 16:44:45.001888220 -0500
+++ asdf.lisp 2015-11-19 14:10:42.703486584 -0500
@@ -3025,7 +3025,9 @@
                                        #+mcl '(:directories t))))
              #+(or abcl xcl) (system:list-directory directory)
              #+cormanlisp (cl::directory-subdirs directory)
- #+genera (fs:directory-list directory))
+ #+genera (handler-case
+ (fs:directory-list directory)
+ (fs:directory-not-found () nil)))
            #+(or abcl allegro cmu genera lispworks sbcl scl xcl)
            (dirs (loop :for x :in dirs
                        :for d = #+(or abcl xcl) (extensions:probe-directory x)

(This has been tested on Portable Genera (formerly Open Genera) running on CentOS 6.)