More robust directory changing

- Doesn't fail when the directory is missing a trailing '/'
     - When directory doesn't exist it signals an informative
       condition.

src/packages.lisp

@@ -8,7 +8,9 @@
   (:import-from :closure-template #:compile-template)
   (:import-from :local-time #:format-rfc1123-timestring)
   (:import-from :uiop #:getcwd
-                      #:chdir)
+                      #:chdir
+                      #:ensure-directory-pathname
+                      #:directory-exists-p)
   (:export #:main
            #:preview
            #:*config*

src/util.lisp

@@ -30,9 +30,17 @@ BODY on files that match the given extension."
                                         #',extension-p
                                         (constantly t))))))
 
+(define-condition directory-does-not-exist (error)
+  ((directory :initarg dir :reader dir))
+  (:report (lambda (c stream)
+             (format stream "The directory '~A' does not exist" (dir c)))))
+
 (defun (setf getcwd) (path)
   "Change the operating system's current directory to PATH."
-  (chdir path)
+  (setf path (ensure-directory-pathname path))
+  (or (and (directory-exists-p path)
+           (chdir path))
+      (error 'directory-does-not-exist :dir path))
   path)
 
 (defmacro with-current-directory (path &body body)