Once again, revert "Use pipes in compiletest"

This reverts commit 1d04b0ed5a.

src/compiletest/compiletest.rs

@@ -8,6 +8,11 @@ import task;
 import core::result;
 import result::{ok, err};
 
+import comm::port;
+import comm::chan;
+import comm::send;
+import comm::recv;
+
 import common::config;
 import common::mode_run_pass;
 import common::mode_run_fail;