Avoid the creation of too many strings in 'package'

Both when setting a path and searching for a file ('searchpath'),
this commit reduces the number of intermediate strings created
in Lua.
(For setting a path the change is not relevant, because this is
done only twice when loading the module. Anyway, it is a nice example
of how to use auxlib buffers to manipulate strings in the C API.)

llimits.h

@@ -39,7 +39,7 @@ typedef signed char ls_byte;
 /* maximum value for size_t */
 #define MAX_SIZET	((size_t)(~(size_t)0))
 
-/* maximum size visible for Lua (must be representable in a lua_Integer */
+/* maximum size visible for Lua (must be representable in a lua_Integer) */
 #define MAX_SIZE	(sizeof(size_t) < sizeof(lua_Integer) ? MAX_SIZET \
                           : (size_t)(LUA_MAXINTEGER))