Remove pre-5.2 Lua varargs syntax (fixes #90)

Author: raboof

ioncore/ioncore_menudb.lua

@@ -44,6 +44,7 @@ end
 -- Define context menu for context \var{ctx}, \var{tab} being a table 
 -- of menu entries.
 function ioncore.defctxmenu(ctx, ...)
+    local arg = {...}
     local tab, add
     if #arg>1 and type(arg[1])=="string" then
         tab=arg[2]

ioncore/ioncore_winprops.lua

@@ -11,6 +11,7 @@ local ioncore=_G.ioncore
 local winprops={}
 
 local function ifnil(...)
+    local arg = {...}
     local n=#arg
     local function nxt(_, i)
         local j=i+1