Floating point exception at exit of debug DR

On Ubuntu 14.04.2 on VirtualBox a user reported this:

```
anon@anon-VirtualBox:~/Desktop$ ~/DrMemory-Linux-1.9.0-RC1B/dynamorio/bin32/drrun -debug -- ./hello.out



Hello world

Floating point exception (core dumped)
```

The FPE is there for DrMem runs as well with -dr_debug.

Not there for release:

```
anon@anon-VirtualBox:~/Desktop$ ~/DrMemory-Linux-1.9.0-RC1B/dynamorio/bin32/drrun -- ./hello.out
Hello world
```