set ack_wildignore to 0 to fix ag startup bug.  ag and ack have different command-line args.  Invoking ag with all of the wildcard ignore flags causes ag to print the help screen instead of the expected version output (since --version is also specified).  A regex in ack.vim is expecting a simple version string but gets a huge help display instead, and ends up emitting a load-time vim error.  wildignore needs to be disabled if using ag to avoid this problem.