Add a benchmark for cross-task kernel memory region synchronization

Vectors are allocated from the kernel's memory region, which has some heinous
synchronization. This is a stress test of vector allocation in many tasks.

src/test/bench/task-perf-vector-party.rs

@@ -0,0 +1,28 @@
+// Vectors are allocated in the Rust kernel's memory region, use of
+// which requires some amount of synchronization. This test exercises
+// that synchronization by spawning a number of tasks and then
+// allocating and freeing vectors.
+
+use std;
+import std::vec;
+import std::uint;
+import std::istr;
+import std::task;
+
+fn f(n: uint) {
+    for each i in uint::range(0u, n) {
+        let v: [u8] = [];
+        vec::reserve(v, 1000u);
+    }
+}
+
+fn main(args: [istr]) {
+    let n = if vec::len(args) < 2u {
+        100u
+    } else {
+        uint::parse_buf(istr::bytes(args[1]), 10u)
+    };
+    for each i in uint::range(0u, 100u) {
+        task::spawn(bind f(n));
+    }
+}