Fix. Easy cleanup unref wrong reference

Fix. Read buffer use size_t as offset
Change. Use httpbin.org as test server

```Lua
-- Test case for easy:close()
form = curl.form()
e = curl.easy{httpheader = {}}
e:close()
form:free()
```

Author: moteus

src/lceasy.c

@@ -87,7 +87,6 @@ static int lcurl_easy_cleanup(lua_State *L){
   p->rbuffer.ref = LUA_NOREF;
 
   for(i = 0; i < LCURL_LIST_COUNT; ++i){
-    luaL_unref(L, LCURL_LUA_REGISTRY, p->lists[i]);
     p->lists[i] = LUA_NOREF;
   }
 
@@ -696,7 +695,7 @@ static size_t lcurl_read_callback(lua_State *L,
   assert(rbuffer->ref == LUA_NOREF);
 
   n = lcurl_util_push_cb(L, rd);
-  lua_pushnumber(L, ret);
+  lua_pushinteger(L, ret);
   if(lua_pcall(L, n, LUA_MULTRET, 0)) return CURL_READFUNC_ABORT;
 
   if(lua_isnoneornil(L, top + 1)){
@@ -786,7 +785,7 @@ static int lcurl_xferinfo_callback(void *arg, curl_off_t dltotal, curl_off_t dln
     if(lua_isboolean(L, top + 1))
       ret = lua_toboolean(L, top + 1)?0:1;
     else{
-      ret = (size_t)lua_tonumber(L, top + 1);
+      ret = lua_tointeger(L, top + 1);
       if(ret == 0) ret = 1; else ret = 0;
     }
   }

src/lcutils.h

@@ -19,8 +19,8 @@ typedef struct lcurl_callback_tag{
 }lcurl_callback_t;
 
 typedef struct lcurl_read_buffer_tag{
-  int ref;
-  int off;
+  int    ref;
+  size_t off;
 }lcurl_read_buffer_t;
 
 int lcurl_storage_init(lua_State *L);

test/test_pause02.c.lua

@@ -5,7 +5,8 @@ local curl = require "lcurl"
 -- i.e. 1 means that CURLPAUSE_CONT will be performed immediately after pause.)
 local WAIT_COUNT   = 32
 
-local RESOURCE_URL = "http://www.rfc-editor.org/rfc/rfc2543.txt"
+local SIZE         = 100 * 1024
+local RESOURCE_URL = "http://httpbin.org/bytes/" .. SIZE
 
 local State = {
   PAUSE   = 0, -- write function should return CURL_WRITEFUNC_PAUSE