rustc: make error messages containing generic more self-explanatory.

Unsuffixed literals like 1 and 1.1, and free type parameters sometimes
have to be printed in error messages, which ended up with <V0>, <VI0>
and <VF0>. This change puts the words "generic" and "integer"/"float"
into the message so it's not a completely black box.

src/librustc/middle/ty.rs

@@ -810,7 +810,7 @@ impl Vid for TyVid {
 }
 
 impl ToStr for TyVid {
-    fn to_str(&self) -> ~str { format!("<V{}>", self.to_uint()) }
+    fn to_str(&self) -> ~str { format!("<generic \\#{}>", self.to_uint()) }
 }
 
 impl Vid for IntVid {
@@ -818,7 +818,7 @@ impl Vid for IntVid {
 }
 
 impl ToStr for IntVid {
-    fn to_str(&self) -> ~str { format!("<VI{}>", self.to_uint()) }
+    fn to_str(&self) -> ~str { format!("<generic integer \\#{}>", self.to_uint()) }
 }
 
 impl Vid for FloatVid {
@@ -826,7 +826,7 @@ impl Vid for FloatVid {
 }
 
 impl ToStr for FloatVid {
-    fn to_str(&self) -> ~str { format!("<VF{}>", self.to_uint()) }
+    fn to_str(&self) -> ~str { format!("<generic float \\#{}>", self.to_uint()) }
 }
 
 impl Vid for RegionVid {

src/test/compile-fail/issue-3680.rs

@@ -10,6 +10,6 @@
 
 fn main() {
     match None {
-        Err(_) => () //~ ERROR mismatched types: expected `std::option::Option<<V1>>` but found `std::result::Result<<V2>,<V3>>`
+        Err(_) => () //~ ERROR mismatched types: expected `std::option::Option<<generic #1>>` but found `std::result::Result<<generic #2>,<generic #3>>`
     }
 }

src/test/compile-fail/issue-4968.rs

@@ -12,5 +12,5 @@
 
 static A: (int,int) = (4,2);
 fn main() {
-    match 42 { A => () } //~ ERROR mismatched types: expected `<VI0>` but found `(int,int)` (expected integral variable but found tuple)
+    match 42 { A => () } //~ ERROR mismatched types: expected `<generic integer #0>` but found `(int,int)` (expected integral variable but found tuple)
 }

src/test/compile-fail/slightly-nice-generic-literal-messages.rs

@@ -0,0 +1,19 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo<T,U>(T);
+
+fn main() {
+    match Foo(1.1) {
+        1 => {}
+        //~^ ERROR expected `Foo<<generic float #0>,<generic #2>>` but found `<generic integer #0>`
+    }
+
+}