Improve wording and spans for unexpected token

* Point at where the token was expected instead of the last token
  successfuly parsed.
* Only show `unexpected token` if the next char and the unexpected token
  don't have the same span.
* Change some cfail and pfail tests to ui test.
* Don't show all possible tokens in span label if they are more than 6.

src/libsyntax_pos/lib.rs

@@ -79,6 +79,12 @@ impl Span {
         Span { lo: BytePos(lo), hi: self.hi, expn_id: self.expn_id}
     }
 
+    /// Returns a new span representing the next character after the end-point of this span
+    pub fn next_point(self) -> Span {
+        let lo = BytePos(cmp::max(self.hi.0, self.lo.0 + 1));
+        Span { lo: lo, hi: lo, expn_id: self.expn_id}
+    }
+
     /// Returns `self` if `self` is not the dummy span, and `other` otherwise.
     pub fn substitute_dummy(self, other: Span) -> Span {
         if self.source_equal(&DUMMY_SP) { other } else { self }