Fix hoogle lookup from local servers

Use a better way to check if the hoogle process is alive: Instead of
checking if the corresponding buffer-name is an alive process, store the
process handle in a global variable and check that.

The problem is that when using 'hoogle-lookup-from-local' without any
hoogle server running, a new local hoogle server is started, but the
code fails to recognize that server is running and instead repeatedly
reports that the server is not running offering to start it.

haskell-mode.el

@@ -859,27 +859,33 @@ is asked to show extra info for the items matching QUERY.."
 (defvar hoogle-server-process-name "emacs-local-hoogle")
 (defvar hoogle-server-buffer-name (format "*%s*" hoogle-server-process-name))
 (defvar hoogle-port-number 49513 "Port number.")
+(defvar hoogle-server-process nil "The process handle of the local hoogle server.")
 
 (defun hoogle-start-server ()
   "Start hoogle local server."
   (interactive)
-  (unless (hoogle-server-live-p)
-    (start-process
-     hoogle-server-process-name
-     (get-buffer-create hoogle-server-buffer-name) "/bin/sh" "-c"
-     (format "hoogle server -p %i" hoogle-port-number))))
+  (if (executable-find "hoogle")
+        (unless (hoogle-server-live-p)
+          (set 'hoogle-server-process
+            (start-process
+               hoogle-server-process-name
+               (get-buffer-create hoogle-server-buffer-name)
+               "/bin/sh" "-c"
+               (format "hoogle server -p %i" hoogle-port-number))))
+    (error "hoogle executable not found")))
 
 (defun hoogle-server-live-p ()
-  "Whether hoogle server is live or not."
+  "Whether the hoogle server process is live."
   (condition-case _err
-      (process-live-p (get-buffer-create hoogle-server-buffer-name))
+      (process-live-p hoogle-server-process)
     (error nil)))
 
 (defun hoogle-kill-server ()
-  "Kill hoogle server if it is live."
+  "Kill the hoogle server if it is live."
   (interactive)
   (when (hoogle-server-live-p)
-    (kill-process (get-buffer-create hoogle-server-buffer-name))))
+    (kill-process (get-buffer-create hoogle-server-buffer-name))
+    (set 'hoogle-server-process nil)))
 
 ;;;###autoload
 (defun hoogle-lookup-from-local ()
@@ -890,10 +896,8 @@ is asked to show extra info for the items matching QUERY.."
                           hoogle-port-number
                           (read-string "hoogle: " (haskell-ident-at-point))))
     (when (y-or-n-p
-           "hoogle server not found, start hoogle server?")
-      (if (executable-find "hoogle")
-          (hoogle-start-server)
-        (error "hoogle is not installed")))))
+           "hoogle server not running, start hoogle server?")
+      (hoogle-start-server))))
 
 ;;;###autoload
 (defcustom haskell-hayoo-url "http://hayoo.fh-wedel.de/?query=%s"