Add SESSION-ALIVE?

scheme/httpd/surflets/packages.scm

@@ -48,6 +48,7 @@
 	  set-options-cache-surflets?!
 
 	  get-sessions
+	  session-alive?
 	  session-surflet-name
 	  session-memo
 	  session-continuation-table

scheme/httpd/surflets/surflet-handler.scm

@@ -387,6 +387,11 @@
     (release-lock *session-table-lock*)
     sessions))
 
+;; SESSION-ALIVE? returns #t if there is a session with this id, #f
+;; otherwise.
+(define (session-alive? session-id)
+  (if (session-lookup session-id) #t #f))
+
 ;;; GET-CONTINUATIONS
 ;; Returns a list of all continuations of the session indicated by the
 ;; SESSION-ID number (locking). The list elements are pairs of