libcore: Use 4x the number of scheduler threads for testing

An arbitrary number. I've done no measurements but it's intended to overcome
the effects of tasks randomly being scheduled to threads and no work stealing.

If scheduler threads == 1 then we just use a single test task.

src/compiletest/compiletest.rs

@@ -187,7 +187,6 @@ fn make_test_closure(cx: cx, testfile: str) -> test::test_fn {
 fn run_test_task(config: common::config,
                  procsrv_chan: procsrv::reqchan,
                  testfile: str) {
-    test::configure_test_task();
 
     let procsrv = procsrv::from_chan(procsrv_chan);
     let cx = {config: config, procsrv: procsrv};

src/libstd/test.rs

@@ -227,7 +227,11 @@ fn run_tests(opts: test_opts, tests: [test_desc],
     }
 }
 
-fn get_concurrency() -> uint { rustrt::sched_threads() }
+fn get_concurrency() -> uint {
+    let threads = rustrt::sched_threads();
+    if threads == 1u { 1u }
+    else { threads * 4u }
+}
 
 fn filter_tests(opts: test_opts,
                 tests: [test_desc]) -> [test_desc] {