Regression test hphp/test/slow/rx/body/fail.php consistently fails

### HHVM Version

lab-3:/data2/swalk/play.121418a/hhvm$ ./hphp/hhvm/hhvm --version
HipHop VM 3.30.0-dev (rel)
Compiler: heads/master-0-g4477e1a390fb2938663a629fe7c81b37f6175d77
Repo schema: ed8df6d7fc054b87e500bd7e541a7222a3a409db

### Operating System and Version

lab-3:/data2/swalk/play.121418a/hhvm$ uname -a
Linux lab-3 4.2.0 #1 SMP Wed Nov 25 14:00:54 CST 2015 aarch64 aarch64 aarch64 GNU/Linux

### Standalone code, or other way to reproduce the problem

hphp/test/run -v -m interp hphp/test/slow/rx/body/fail.php

### Actual result

lab-3:/data2/swalk/play.121418a/hhvm$ hphp/test/run -v -m interp hphp/test/slow/rx/body/fail.php
You are using the binary located at: ./hphp/hhvm/hhvm
Running 1 tests in 1 threads (0 in serial)

Warning: Compilation failed: missing ) at offset 118 in /data2/swalk/play.121418a/hhvm/hphp/test/run.php on line 1748

Warning: Compilation failed: missing ) at offset 118 in /data2/swalk/play.121418a/hhvm/hphp/test/run.php on line 1748

Warning: Compilation failed: unmatched parentheses at offset 1 in /data2/swalk/play.121418a/hhvm/hphp/test/run.php on line 1748
hphp/test/slow/rx/body/fail.php FAILED (3.38s)

1 tests failed

### Expected result

pass

I'm not sure why it's crying about the (unchanged) driver, but it looks like
the actual output does not match the fail.php.expectregex file when you
compare manually.

I think this was introduced by https://github.com/facebook/hhvm/commit/d46a624307a846d56a2381034f4c0732bed3749a

Run hphp/test/run -v -m interp hphp/test/slow/rx/body/fail.php and compare its output with hphp/test/slow/rx/body/fail.php.expectregex. Inspect the referenced hphp/test/run.php line 1748 and commit d46a624307a846d56a2381034f4c0732bed3749a to determine why the unchanged driver reports compilation warnings. Done means the regression test passes and matches its expected output.

Written by the indexing model from the issue text.