ShebangDirective should be unconditionally parsed

[333fred]

Right now, if the #! is not at the very first character of a file, it will not be parsed as a shebang directive:

roslyn/src/Compilers/CSharp/Portable/Parser/DirectiveParser.cs

Lines 111 to 114 in 256273c

	if (contextualKind == SyntaxKind.ExclamationToken && hashPosition == 0 && !hash.HasTrailingTrivia)
	{
	result = this.ParseShebangDirective(hash, this.EatToken(SyntaxKind.ExclamationToken), isActive);
	}

. This is not good error recovery and will likely make it more difficult for consumers to have analyzers/fixers for this syntax when it is misplaced. We should instead report an error and always parse as a shebang.