Make passing invalid options to install.rb fatal

In b909b67 the --[no-]prereq-checks
option was dropped. The error was printed, but then continued to execute
and it ignored all passed options. That caused a regression in 8.21.0.

It now catches the error and exits with a non-zero exit code, forcing
the packager to deal with it.

Author: ekohl

install.rb

@@ -159,6 +159,9 @@ def prepare_installation
     end
 
     opts.parse!
+  rescue OptionParser::InvalidOption => e
+    $stderr.puts e
+    exit 1
   end
 
   # Mac OS X 10.5 and higher declare bindir