Added handle_t type to server interface so that we can make handles
pointers later on.
Always use 0 to signal invalid handle in server requests.

diff --git a/scheduler/thread.c b/scheduler/thread.c
index 7aca5d2..cea1156 100644
--- a/scheduler/thread.c
+++ b/scheduler/thread.c
@@ -58,7 +58,7 @@
     SERVER_START_REQ
     {
         struct get_thread_info_request *req = server_alloc_req( sizeof(*req), 0 );
-        req->handle = -1;
+        req->handle = 0;
         req->tid_in = (void *)id;
         if (!server_call_noerr( REQ_GET_THREAD_INFO )) ret = req->teb;
     }
@@ -284,7 +284,8 @@
                             LPTHREAD_START_ROUTINE start, LPVOID param,
                             DWORD flags, LPDWORD id )
 {
-    int socket = -1, handle = -1;
+    int socket = -1;
+    HANDLE handle = 0;
     TEB *teb;
     void *tid = 0;
 
@@ -302,7 +303,7 @@
         }
     }
     SERVER_END_REQ;
-    if (handle == -1) return 0;
+    if (!handle) return 0;
 
     if (!(teb = THREAD_Create( socket, stack, TRUE )))
     {