'use std' in module imported by crate corrupts things

[jyasskin]

$ cat ~/tmp/test.rc
use std;
mod driver;
$ cat ~/tmp/driver.rs
use std;
import std._vec;
fn main(vec[str] args) -> () {
  log ("args(0) == " + args.(0));
  log _vec.slice[str](args, 0, 1).(0);
}
$ ./rustboot -L . ~/tmp/test.rc -o ~/tmp/test && ~/tmp/test abc
rt: 0xa0563720:0xbfffec74:0x00100200:     upcall log_str("args(0) == /Users/jyasskin/tmp/test")
rt: fatal, 'leaked memory in rust main loop (2 objects)' failed, rt/rust.cpp:32

Commenting out the "use std;" in driver.rs fixes the leak and keeps running through the second log statement. I saw this first as a SIGBUS, but I suspect this reduction is the same bug.

[graydon]

WONTFIX (not required for bootstrapping).