add a new AST dumper interface (E->dump()). This dumps out

the AST in a structural, non-pretty, form useful for understanding
the AST.  It isn't quite done yet, but is already somewhat useful.

For this example:

int test(short X, long long Y) {
  return X < ((100));
}

we get (with -parse-ast-dump):

int test(short X, long long Y)
(CompoundStmt 0x2905ce0
  (ReturnStmt 0x2905cd0
    (BinaryOperator 0x2905cb0 '<'
      (ImplicitCastExpr 0x2905ca0
        (DeclRefExpr 0x2905c20 Decl='X' 0x2905bb0))
      (ParenExpr 0x2905c80
        (ParenExpr 0x2905c60
          (IntegerLiteral 0x2905c40 100))))))

llvm-svn: 40954