Add lua_wrapper for dynamical loading liblua while loading lua plugin

Little wrapper to fix some issues with loading luasocket & other lua C-libraries. Although plugin already linked with liblua.so, some users reported that C-libraries couldn't find lua library functions (lua_insert etc).

You may solve this by defining full path to liblua.so in LD_PRELOAD environment variable. Another way is to load empty wrapper linked with liblua during plugin loading. This way is implemented in this pull request.

Inspired by python plugin (uses same way). Originally developerd [here](http://verlihub.aliki.ru/forum/viewtopic.php?f=4&t=652) (in russian).