Warn on invalided FSI directives.

[KevinRansom]

While working on the packagemanager a bit. I felt the need to clean up some of the code around directives.

Most especially this:

            | IHash (ParsedHashDirective(c,arg,_),_) -> 
                fsiConsoleOutput.uprintfn "%s" (FSIstrings.SR.fsiInvalidDirective(c, String.concat " " arg))  // REVIEW: uprintnfnn - like other directives above
                istate,Completed None  (* REVIEW: cont = CompletedWithReportedError *)

If the #directive is invalid, we just printout a message in white and then move on.

E.g.

Note, that the code before and after the definition is still compiled and executed.

I decided to turn it into a warning, so that existing scripts that relied on us not failing would still continue to work.

[cartermp]

Good improvement!

[brettfo]

Minor suggestion: copy over the localized strings, since we know they're correct.