Add improvements to insert_with_key

This commit adds a lower-level implementation of the generic
`insert_with_key` which I expect to be faster. Now insert could be
defined with insert_with_key, too, although I'm not sure we want to do that.

This also clarifies the tests a bit and adds an `insert_with` function.

src/test/bench/shootout-k-nucleotide-pipes.rs

@@ -69,7 +69,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    mm.insert_with_key(|k,v,v1| {v + v1}, key, 1);
+    mm.insert_with(key, 1, |v,v1| { v+v1 });
 }
 
 // given a ~[u8], for each window call a function

src/test/bench/shootout-k-nucleotide.rs

@@ -66,7 +66,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    mm.insert_with_key(|k,v,v1| {v + v1}, key, 1);
+    mm.insert_with(key, 1, |v,v1| { v+v1 });
 }
 
 // given a ~[u8], for each window call a function

src/test/run-pass/class-impl-very-parameterized-trait.rs

@@ -61,13 +61,20 @@ impl<T: Copy> cat<T> : Map<int, T> {
      else { None }
   }
 
-  fn insert_with_key(ff: fn(+k: int, +v0: T, +v1: T) -> T, +key: int, +val: T) -> bool {
+  fn insert_with_key(+key: int, +val: T, ff: fn(+k: int, +v0: T, +v1: T) -> T) -> bool {
     match self.find(key) {
       None            => return self.insert(key, val),
       Some(copy orig) => return self.insert(key, ff(key, orig, val))
     }
   }
 
+  fn insert_with(+key: int, +val: T, ff: fn(+v0: T, +v1: T) -> T) -> bool {
+    match self.find(key) {
+      None            => return self.insert(key, val),
+      Some(copy orig) => return self.insert(key, ff(orig, val))
+    }
+  }
+
 
   fn remove(+k:int) -> bool {
     match self.find(k) {