don't source rest of file if no lua or correct version

If lua is not there the script continues to execute and that creates a lot of errors when editing text like for example:

function neocomplete#handler#_do_auto_complete..neocomplete#complete#_set_results_pos..12..neocompl
ete#get_keyword_pattern_end..neocomplete#get_keyword_pattern..neocomplete#helper#unite_patterns, li
ne 3
Press ENTER or type command to continue

a lot of this messages appear. This seems to fix it.