Mysterious runtime races when running stage1-coretest

[bblum]

One, an assertion in the random number generator - stack trace: http://pastebin.mozilla.org/1700653

Another, a segmentation fault in rust_env_pairs - stack trace: http://pastebin.mozilla.org/1700654

These are pretty rare - in 100 tries under gdb, the first one happened 3 times, and the second 1 time.

I found these after submitting linked failure in rust (5d6d3d0), but verified they existed before, too (at 424ae44).

[bblum]

For the second one, I present for your due amusement the following command, which makes it obvious:

true;
while [ "$?" = "0" ]; do
    ./x86_64-unknown-linux-gnu/test/coretest.stage1-x86_64-unknown-linux-gnu setenv;
done

[bblum]

First one, graydon says is not a race but just a short-read, and the assert was wrong.