Add two new Token helper functions, "is" and "isNot". This allows us to write

stuff like this:

       // If we don't have a comma, it is either the end of the list (a ';') or
       // an error, bail out.
       if (Tok.isNot(tok::comma))
         break;
instead of:
       // If we don't have a comma, it is either the end of the list (a ';') or
       // an error, bail out.
       if (Tok.getKind() != tok::comma)
         break;

There is obviously no functionality change, but the code reads a bit better and is 
more terse.

llvm-svn: 42795