This should allow tests to run for 20 minutes without producing any
output (usually, the travis build woud fail after 10 minutes without any
output).

Since the packages are not whitelisted, we need to do this by hand...
Thx travis!

This reverts commit 86db8b736cba53de22acbd7a4e6cafc6ba0a1eaa, as these
packages are disallowed on travis.

Some of the travis builders run out of memory during compilation of the
tests:
```
virtual memory exhausted: Cannot allocate memory
```
Let's see if we can get rid of that problem an still stay below the 50min
timeout.

This reverts commit 16c8156eb25937f9a073813e6edd8df411081f0f.

This reverts commit 7fa44f8e87c7a4eb48d0c1eb245747b03b806581.

This reverts commit df22d767b0ca93181064d643fb623f34d66a9d1f.

External libraries are always built with release flags.