writing tests to validate the parser using shelltest

Following the major change enabling tests:

Adding a new streaming protocol: stdin://

  This protocol has a couple of issues. As the lexer is LL(2), it is
  very unlikely that the parser can be used interactively.

Writing validate.c binary

  A simple program that simply validates configuration
  files. Incidentally, it is also used for testing the parser.

Adding shelltest [http://joyful.com/shelltestrunner/] dependency

  Used to write acceptance tests