PR#6060: Add some missing compiler options to ocamlbuild. (Patch by Anil Madhavapeddy!)
    
    * -short-paths is activated via the "short_paths" tag
    * -principal is activated via the "principal" tag
    * -strict_sequence now has a "strict_sequence" tag to alias the
      "strict-sequence" tag that was already there, to follow the
      convention of command-line options having dashes replaced by
      underscores.  It's easy to mess this up since incorrect tags
      are silently ignored by ocamlbuild.
    
    Add test cases that check if principal and strict-sequence have
    been passed, and tweak the test suite slightly to make it easier
    to match on failing_msg output.
    
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.01@13865 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02